Light-emitting device, display device, light-emitting apparatus, electronic device, and lighting device

ABSTRACT

A light-emitting device with high emission efficiency is provided. The light-emitting device includes an EL layer and a light-transmitting electrode. The EL layer includes a light-emitting layer and a low refractive index layer. The low refractive index layer is positioned between the light-emitting layer and the light-transmitting electrode. A cap layer is in contact with a surface of the light-transmitting electrode on the side opposite to the EL layer. The cap layer includes a high refractive index material having an ordinary refractive index of higher than or equal to 1.90 and lower than or equal to 2.40 and an ordinary extinction coefficient of higher than or equal to 0 and lower than or equal to 0.01. The low refractive index layer includes a low refractive index material having an ordinary refractive index of higher than or equal to 1.60 and lower than or equal to 1.70.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to an organic compound,a light-emitting element, a light-emitting device, a display module, alighting module, a display device, a light-emitting apparatus, anelectronic device, a lighting device, and an electronic appliance. Notethat one embodiment of the present invention is not limited to the abovetechnical field. The technical field of one embodiment of the inventiondisclosed in this specification and the like relates to an object, amethod, or a manufacturing method. One embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specifically, examples of the technical field of oneembodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a liquid crystaldisplay device, a light-emitting apparatus, a lighting device, a powerstorage device, a memory device, an imaging device, a driving methodthereof, and a manufacturing method thereof.

2. Description of the Related Art

Light-emitting devices (organic EL devices) including organic compoundsand utilizing electroluminescence (EL) have been put to more practicaluse. In the basic structure of such light-emitting devices, an organiccompound layer containing a light-emitting material (an EL layer) issandwiched between a pair of electrodes. Carriers are injected byapplication of a voltage to the device, and recombination energy of thecarriers is used, whereby light emission can be obtained from thelight-emitting material.

Such light-emitting devices are of self-luminous type and thus haveadvantages over liquid crystal displays, such as high visibility and noneed for a backlight when used as pixels of a display, and areparticularly suitable for flat panel displays. Displays including suchlight-emitting devices are also highly advantageous in that they can bethin and lightweight. Moreover, such light-emitting devices also have afeature that the response speed is extremely fast.

Since light-emitting layers of such light-emitting devices can besuccessively formed two-dimensionally, planar light emission can beachieved. This feature is difficult to realize with point light sourcestypified by incandescent lamps or LEDs or linear light sources typifiedby fluorescent lamps; thus, such light-emitting devices also have agreat potential as planar light sources which can be applied to lightingdevices and the like.

Displays or lighting devices including light-emitting devices aresuitable for a variety of electronic devices as described above, andresearch and development of light-emitting devices have progressed formore favorable characteristics.

Low outcoupling efficiency is often a problem in an organic EL device.In order to improve the outcoupling efficiency, a structure including alayer formed using a low refractive index material in an EL layer (seePatent Document 1, for example) has been proposed.

REFERENCE Patent Document

[Patent Document 1] United States Patent Application Publication No.2020/0176692

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide alight-emitting device with high emission efficiency. Another object ofone embodiment of the present invention is to provide any of alight-emitting device, a light-emitting apparatus, an electronic device,a display device, and an electronic appliance each having low powerconsumption.

It is only necessary that at least one of the above-described objects beachieved in the present invention.

One embodiment of the present invention is a material for a cap layer ofa light-emitting device, which has an ordinary refractive index ofhigher than or equal to 1.90 and lower than or equal to 2.40 and anordinary extinction coefficient of higher than or equal to 0 and lowerthan or equal to 0.01, at any wavelength in the range from 455 nm to 465nm.

Another embodiment of the present invention is a material for a caplayer of a light-emitting device, which has an ordinary refractive indexof higher than or equal to 1.90 and lower than or equal to 2.40 and anordinary extinction coefficient of higher than or equal to 0 and lowerthan or equal to 0.01, in the entire wavelength range from 455 nm to 465nm.

In any of the above-described embodiments of the present invention, theordinary refractive index is preferably higher than or equal to 1.95 andlower than or equal to 2.40.

Another embodiment of the present invention is a material for a caplayer of a light-emitting device, which has an ordinary refractive indexof higher than or equal to 1.85 and lower than or equal to 2.40 and anordinary extinction coefficient of higher than or equal to 0 and lowerthan or equal to 0.01, at any wavelength in the range from 500 nm to 650nm.

Another embodiment of the present invention is a material for a caplayer of a light-emitting device, which has an ordinary refractive indexof higher than or equal to 1.85 and lower than or equal to 2.40 and anordinary extinction coefficient of higher than or equal to 0 and lowerthan or equal to 0.01, in the entire wavelength range from 500 nm to 650nm.

In any of the above-described embodiments of the present invention, theordinary refractive index is preferably higher than or equal to 1.90 andlower than or equal to 2.40.

In any of the above-described embodiments of the present invention, thematerial preferably includes a condensed ring skeleton having four ormore rings.

In any of the above-described embodiments of the present invention, thematerial preferably includes a condensed ring skeleton having five ormore rings.

In any of the above-described embodiments of the present invention, thematerial preferably includes a sulfur atom.

In any of the above-described embodiments of the present invention, anevaporated film of the material preferably has large anisotropy.

In any of the above-described embodiments of the present invention, analignment order parameter of an evaporated film of the material, whichis calculated from an ordinary extinction coefficient peak positioned onthe longest wavelength side, is preferably less than or equal to −0.1.

Another embodiment of the present invention is a cap layer of alight-emitting device. The light-emitting device includes an EL layerbetween a pair of electrodes including a light-transmitting electrode.The cap layer is in contact with a surface of the light-transmittingelectrode on the side opposite to the EL layer. The cap layer includes amaterial having an ordinary refractive index of higher than or equal to1.90 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to0.01, at any wavelength in the range from 455 nm to 465 nm.

Another embodiment of the present invention is a cap layer of alight-emitting device. The light-emitting device includes an EL layerbetween a pair of electrodes including a light-transmitting electrode.The cap layer is in contact with a surface of the light-transmittingelectrode on the side opposite to the EL layer. The cap layer includes amaterial having an ordinary refractive index of higher than or equal to1.90 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to0.01, in the entire wavelength range from 455 nm to 465 nm.

Another embodiment of the present invention is a cap layer of alight-emitting device. The light-emitting device includes an EL layerbetween a pair of electrodes including a light-transmitting electrode.The cap layer is in contact with a surface of the light-transmittingelectrode on the side opposite to the EL layer. Light emitted by thelight-emitting device has a peak wavelength of higher than or equal to455 nm and lower than or equal to 465 nm. The cap layer includes amaterial having an ordinary refractive index of higher than or equal to1.90 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to0.01, at the peak wavelength.

In any of the above-described embodiments of the present invention, thematerial preferably has an ordinary extinction coefficient of higherthan 0.05 at any wavelength in the range from 370 nm to 700 nm.

In any of the above-described embodiments of the present invention, theordinary refractive index of the material is preferably higher than orequal to 1.95 and lower than or equal to 2.40.

Another embodiment of the present invention is a cap layer of alight-emitting device. The light-emitting device includes an EL layerbetween a pair of electrodes including a light-transmitting electrode.The cap layer is in contact with a surface of the light-transmittingelectrode on the side opposite to the EL layer. The cap layer includes amaterial having an ordinary refractive index of higher than or equal to1.85 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to0.01, at any wavelength in the range from 500 nm to 650 nm.

Another embodiment of the present invention is a cap layer of alight-emitting device. The light-emitting device includes an EL layerbetween a pair of electrodes including a light-transmitting electrode.The cap layer is in contact with a surface of the light-transmittingelectrode on the side opposite to the EL layer. The cap layer includes amaterial having an ordinary refractive index of higher than or equal to1.85 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to0.01, in the entire wavelength range from 500 nm to 650 nm.

Another embodiment of the present invention is a cap layer of alight-emitting device. The light-emitting device includes an EL layerbetween a pair of electrodes including alight-transmitting electrode.The cap layer is in contact with a surface of the light-transmittingelectrode on the side opposite to the EL layer. Light emitted by thelight-emitting device has a peak wavelength of higher than or equal to500 nm and lower than or equal to 650 nm. The cap layer includes amaterial having an ordinary refractive index of higher than or equal to1.85 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to0.01, at the peak wavelength.

In any of the above-described embodiments of the present invention, thematerial preferably has an ordinary extinction coefficient of higherthan 0.05 at any wavelength in the range from 370 nm to 700 nm.

In any of the above-described embodiments of the present invention, theordinary refractive index of the material is preferably higher than orequal to 1.90 and lower than or equal to 2.40.

In any of the above-described embodiments of the present invention, thematerial preferably includes a condensed ring skeleton having four ormore rings.

In any of the above-described embodiments of the present invention, thematerial preferably includes a condensed ring skeleton having five ormore rings.

In any of the above-described embodiments of the present invention, thematerial preferably includes a sulfur atom.

In any of the above-described embodiments of the present invention, anevaporated film of the material preferably has large anisotropy.

In any of the above-described embodiments of the present invention, analignment order parameter of an evaporated film of the material, whichis calculated from an ordinary extinction coefficient peak positioned onthe longest wavelength side, is preferably less than or equal to −0.1.

Another embodiment of the present invention is a light-emitting deviceincluding an EL layer between a pair of electrodes. One of the pair ofelectrodes is a light-transmitting electrode. The EL layer includes atleast a light-emitting layer and a low refractive index layer. A caplayer is in contact with a surface of the light-transmitting electrodeon the side opposite to the EL layer. The cap layer includes a highrefractive index material having an ordinary refractive index of higherthan or equal to 1.90 and lower than or equal to 2.40 and an ordinaryextinction coefficient of higher than or equal to 0 and lower than orequal to 0.01 at any wavelength in the range from 455 nm to 465 nm. Thelow refractive index layer includes a low refractive index materialhaving an ordinary refractive index of higher than or equal to 1.50 andlower than or equal to 1.75 at any wavelength in the range from 455 nmto 465 nm.

Another embodiment of the present invention is a light-emitting deviceincluding an EL layer between a pair of electrodes. One of the pair ofelectrodes is a light-transmitting electrode. The EL layer includes atleast a light-emitting layer and a low refractive index layer. A caplayer is in contact with a surface of the light-transmitting electrodeon the side opposite to the EL layer. The cap layer includes a highrefractive index material having an ordinary refractive index of higherthan or equal to 1.90 and lower than or equal to 2.40 and an ordinaryextinction coefficient of higher than or equal to 0 and lower than orequal to 0.01 in the entire wavelength range from 455 nm to 465 nm. Thelow refractive index layer includes a low refractive index materialhaving an ordinary refractive index of higher than or equal to 1.50 andlower than or equal to 1.75 at any wavelength in the range from 455 nmto 465 nm.

Another embodiment of the present invention is a light-emitting deviceincluding an EL layer between a pair of electrodes. One of the pair ofelectrodes is a light-transmitting electrode. The EL layer includes atleast a light-emitting layer and a low refractive index layer. A caplayer is in contact with a surface of the light-transmitting electrodeon the side opposite to the EL layer. Light emitted by thelight-emitting device has a peak wavelength of higher than or equal to455 nm and lower than or equal to 465 nm. The cap layer includes a highrefractive index material having an ordinary refractive index of higherthan or equal to 1.90 and lower than or equal to 2.40 and an ordinaryextinction coefficient of higher than or equal to 0 and lower than orequal to 0.01 at the peak wavelength. The low refractive index layerincludes a low refractive index material having an ordinary refractiveindex of higher than or equal to 1.50 and lower than or equal to 1.75 atthe peak wavelength.

In any of the above-described embodiments of the present invention, thelow refractive index layer is preferably positioned between thelight-emitting layer and the light-transmitting electrode.

In any of the above-described embodiments of the present invention, thehigh refractive index material preferably has an ordinary extinctioncoefficient of higher than 0.01 at wavelengths of lower than or equal to390 nm.

In any of the above-described embodiments of the present invention, theordinary refractive index of the high refractive index material ispreferably higher than or equal to 1.95 and lower than or equal to 2.40.

Another embodiment of the present invention is a light-emitting deviceincluding an EL layer between a pair of electrodes. One of the pair ofelectrodes is a light-transmitting electrode. The EL layer includes atleast a light-emitting layer and a low refractive index layer. The lowrefractive index layer is positioned between the light-emitting layerand the light-transmitting electrode. A cap layer is in contact with asurface of the light-transmitting electrode on the side opposite to theEL layer. The cap layer includes a high refractive index material havingan ordinary refractive index of higher than or equal to 1.85 and lowerthan or equal to 2.40 and an ordinary extinction coefficient of higherthan or equal to 0 and lower than or equal to 0.01 at any wavelength inthe range from 500 nm to 650 nm. The low refractive index layer includesa low refractive index material having an ordinary refractive index ofhigher than or equal to 1.45 and lower than or equal to 1.70 in theentire wavelength range from 500 nm to 650 nm.

Another embodiment of the present invention is a light-emitting deviceincluding an EL layer between a pair of electrodes. One of the pair ofelectrodes is a light-transmitting electrode. The EL layer includes atleast a light-emitting layer and a low refractive index layer. The lowrefractive index layer is positioned between the light-emitting layerand the light-transmitting electrode. A cap layer is in contact with asurface of the light-transmitting electrode on the side opposite to theEL layer. The cap layer includes a high refractive index material havingan ordinary refractive index of higher than or equal to 1.85 and lowerthan or equal to 2.40 and an ordinary extinction coefficient of higherthan or equal to 0 and lower than or equal to 0.01 in the entirewavelength range from 500 nm to 650 nm. The low refractive index layerincludes a low refractive index material having an ordinary refractiveindex of higher than or equal to 1.45 and lower than or equal to 1.70 inthe entire wavelength range from 500 nm to 650 nm.

Another embodiment of the present invention is a light-emitting deviceincluding an EL layer between a pair of electrodes. One of the pair ofelectrodes is a light-transmitting electrode. The EL layer includes atleast a light-emitting layer and a low refractive index layer. The lowrefractive index layer is positioned between the light-emitting layerand the light-transmitting electrode. Light emitted by thelight-emitting device has a peak wavelength of higher than or equal to500 nm and lower than or equal to 650 nm. A cap layer is in contact witha surface of the light-transmitting electrode on the side opposite tothe EL layer. The cap layer includes a high refractive index materialhaving an ordinary refractive index of higher than or equal to 1.85 andlower than or equal to 2.40 and an ordinary extinction coefficient ofhigher than or equal to 0 and lower than or equal to 0.01 at the peakwavelength. The low refractive index layer includes a low refractiveindex material having an ordinary refractive index of higher than orequal to 1.45 and lower than or equal to 1.70 at the peak wavelength.

In any of the above-described embodiments of the present invention, thehigh refractive index material preferably has an ordinary extinctioncoefficient of higher than 0.05 at any wavelength in the range from 370nm to 700 nm.

In any of the above-described embodiments of the present invention, theordinary refractive index of the high refractive index material ispreferably higher than or equal to 1.90 and lower than or equal to 2.40.

In any of the above-described embodiments of the present invention, thelight-transmitting electrode is preferably a cathode.

In any of the above-described embodiments of the present invention, thelow refractive index layer is preferably in an electron-transportregion.

In any of the above-described embodiments of the present invention, thelow refractive index layer is preferably an electron-transport layer.

In any of the above-described embodiments of the present invention, thelow refractive index material is preferably a material having anelectron-transport property.

In any of the above-described embodiments of the present invention, thelow refractive index material is preferably a mixed material of amaterial having an electron-transport property and a metal complex.

In any of the above-described embodiments of the present invention, theother of the pair of electrodes is preferably a reflective electrode,the EL layer preferably includes a second low refractive index layerbetween the light-emitting layer and the reflective electrode, and thesecond low refractive index layer preferably includes a second lowrefractive index material having an ordinary refractive index of higherthan or equal to 1.50 and lower than or equal to 1.75 at a peakwavelength of light emitted by the light-emitting device.

In the above-described embodiment of the present invention, the secondlow refractive index layer is preferably in a hole-transport region.

In any of the above-described embodiments of the present invention, thesecond low refractive index layer is preferably a hole-transport layer.

In any of the above-described embodiments of the present invention, thesecond low refractive index material is preferably a material having ahole-transport property.

In any of the above-described embodiments of the present invention, thehigh refractive index material preferably includes a condensed ringskeleton having four or more rings.

In any of the above-described embodiments of the present invention, thehigh refractive index material preferably includes a condensed ringskeleton having five or more rings.

In any of the above-described embodiments of the present invention, thehigh refractive index material preferably includes a sulfur atom.

In any of the above-described embodiments of the present invention, anevaporated film of the high refractive index material preferably haslarge anisotropy.

In any of the above-described embodiments of the present invention, analignment order parameter of an evaporated film of the high refractiveindex material, which is calculated from an ordinary extinctioncoefficient peak positioned on the longest wavelength side, ispreferably less than or equal to −0.1.

Another embodiment of the present invention is an electronic deviceincluding any of the above-described light-emitting devices, a sensor,an operation button, and a speaker or a microphone.

Another embodiment of the present invention is a light-emittingapparatus including any of the above-described light-emitting devices,and a transistor or a substrate.

Another embodiment of the present invention is a display deviceincluding any of the above-described light-emitting devices, and atransistor or a substrate.

Another embodiment of the present invention is a lighting deviceincluding any of the above-described light-emitting devices and ahousing.

Note that the light-emitting apparatus in this specification includes,in its category, an image display device that uses a light-emittingdevice. The light-emitting apparatus may also include a module in whicha light-emitting device is provided with a connector such as ananisotropic conductive film or a tape carrier package (TCP), a module inwhich a printed wiring board is provided at the end of a TCP, and amodule in which an integrated circuit (IC) is directly mounted on alight-emitting device by a chip on glass (COG) method. Furthermore, alighting device or the like may include the light-emitting apparatus.

With one embodiment of the present invention, a light-emitting devicewith high emission efficiency can be provided. With one embodiment ofthe present invention, any of a light-emitting device, a light-emittingapparatus, an electronic device, a display device, and an electronicappliance each having low power consumption can be provided.

Note that the description of these effects does not preclude theexistence of other effects. One embodiment of the present invention doesnot need to have all these effects. Other effects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. TA to FIG. 1D each schematically illustrate a light-emittingdevice;

FIGS. 2A and 2B illustrate an active matrix light-emitting apparatus;

FIGS. 3A and 3B each illustrate an active matrix light-emittingapparatus;

FIG. 4 illustrates an active matrix light-emitting apparatus;

FIGS. 5A and 5B illustrate a passive matrix light-emitting apparatus;

FIGS. 6A and 6B illustrate a lighting device;

FIGS. 7A, 7B1, 7B2, and 7C illustrate electronic devices;

FIGS. 8A to 8C illustrate electronic devices;

FIG. 9 illustrates a lighting device;

FIG. 10 illustrates a lighting device;

FIG. 11 illustrates in-vehicle display devices and lighting devices;

FIGS. 12A and 12B illustrate an electronic device;

FIGS. 13A to 13C illustrate an electronic device;

FIGS. 14A to 14D illustrate a structure example of a display device;

FIGS. 15A to 15F illustrate an example of a manufacturing method of adisplay device;

FIGS. 16A to 16F illustrate the example of the manufacturing method ofthe display device.

FIGS. 17A and 17B show a change in blue index (BI) depending on thepresence or absence of low refractive index layers in bluelight-emitting devices with a varying ordinary refractive index of a caplayer;

FIG. 18 shows ordinary and extraordinary refractive indexes ofmmtBuBioFBi, mmtBumBPTzn, and Li-6mq;

FIG. 19 shows ordinary and extraordinary refractive indexes and ordinaryand extraordinary extinction coefficients of BisBTc and DBT3P-II;

FIG. 20 shows luminance-current density characteristics of alight-emitting device 1 and a comparative light-emitting device 1;

FIG. 21 shows luminance-voltage characteristics of the light-emittingdevice 1 and the comparative light-emitting device 1;

FIG. 22 shows current efficiency-luminance characteristics of thelight-emitting device 1 and the comparative light-emitting device 1;

FIG. 23 shows current density-voltage characteristics of thelight-emitting device 1 and the comparative light-emitting device 1;

FIG. 24 shows blue index-luminance characteristics of the light-emittingdevice 1 and the comparative light-emitting device 1;

FIG. 25 shows emission spectra of the light-emitting device 1 and thecomparative light-emitting device 1;

FIG. 26 shows changes in relative luminance over time of thelight-emitting device 1 and the comparative light-emitting device 1;

FIG. 27 shows relationships between the thickness of a cap layer and themaximum blue index value of light-emitting devices 1-1 to 1-4 andcomparative light-emitting devices 1-1 to 1-4;

FIG. 28 shows ordinary and extraordinary refractive indexes ofmmtBumTPoFBi-04 and BBA(βN2)B-03;

FIG. 29 shows luminance-current density characteristics of alight-emitting device 10;

FIG. 30 shows luminance-voltage characteristics of the light-emittingdevice 10;

FIG. 31 shows current efficiency-luminance characteristics of thelight-emitting device 10;

FIG. 32 shows current density-voltage characteristics of thelight-emitting device 10;

FIG. 33 shows blue index-luminance characteristics of the light-emittingdevice 10;

FIG. 34 shows an emission spectrum of the light-emitting device 10; and

FIG. 35 shows a change in relative luminance over time of thelight-emitting device 10.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the drawings. Note that the present invention is notlimited to the following description, and it will be readily appreciatedby those skilled in the art that modes and details of the presentinvention can be modified in various ways without departing from thespirit and scope of the present invention. Therefore, the presentinvention should not be construed as being limited to the description inthe following embodiments.

Note that in the case where light is incident on a material havingoptical anisotropy, light with a plane of vibration parallel to theoptical axis is referred to as extraordinary light (rays) and light witha plane of vibration perpendicular to the optical axis is referred to asordinary light (rays); the refractive index of the material with respectto ordinary light might differ from that with respect to extraordinarylight. In such a case, the ordinary refractive index and theextraordinary refractive index can be separately calculated byanisotropy analysis. Note that in the case where the measured materialhas both the ordinary refractive index and the extraordinary refractiveindex, the ordinary refractive index is used as an index in thisspecification. Furthermore, when simply mentioning a refractive index,the refractive index refers to the average value of the ordinaryrefractive index and the extraordinary refractive index.

As is the case with the refractive index, the extinction coefficientwith respect to ordinary light might differ from that with respect toextraordinary light, and the ordinary extinction coefficient and theextraordinary extinction coefficient can be separately calculated byanisotropy analysis. In the case where the measured material has boththe ordinary extinction coefficient and the extraordinary extinctioncoefficient, the ordinary extinction coefficient is used as an index inthis specification. Furthermore, when simply mentioning an extinctioncoefficient, the extinction coefficient refers to the average value ofthe ordinary extinction coefficient and the extraordinary extinctioncoefficient.

Furthermore, an evaporated film in this specification refers to a filmdeposited by an evaporation method in the state where a substrate is atroom temperature.

Embodiment 1

FIG. TA illustrates a light-emitting device 600 of one embodiment of thepresent invention. Light-emitting devices illustrated in FIGS. 1A to 1Deach include a first electrode 101, a second electrode 102, an EL layer103, and a cap layer 155. The EL layer 103 includes at least alight-emitting layer 113 and preferably further includes a lowrefractive index layer 156.

The second electrode 102 is a light-transmitting electrode, and thelight-emitting device 600 emits light from the second electrode 102side.

In the EL layer 103, a region between the light-emitting layer 113 andthe first electrode 101 is referred to as a carrier-transport region150, and a region between the light-emitting layer 113 and the secondelectrode 102 is referred to as a carrier-transport region 151; one ofthe regions is a hole-transport region and the other is anelectron-transport region. The low refractive index layer 156 ispreferably provided in the carrier-transport region 151.

The second electrode 102 is provided in contact with and sandwichedbetween the EL layer 103 and the cap layer 155.

The cap layer 155 has a high refractive index. Specifically, theordinary refractive index of the cap layer 155 at any wavelength in therange from 455 nm to 465 nm, preferably in the entire wavelength rangefrom 455 nm to 465 nm, is preferably higher than or equal to 1.90 andlower than or equal to 2.40, further preferably higher than or equal to1.95 and lower than or equal to 2.40. Furthermore, the ordinaryextinction coefficient of the cap layer at any wavelength in the rangefrom 455 nm to 465 nm, preferably in the entire wavelength range from455 nm to 465 nm, is preferably higher than or equal to 0 and lower thanor equal to 0.01.

Alternatively, the ordinary refractive index of the cap layer 155 at anywavelength in the range from 500 nm to 650 nm, preferably in the entirewavelength range from 500 nm to 650 nm, is preferably higher than orequal to 1.85 and lower than or equal to 2.40, further preferably higherthan or equal to 1.90 and lower than or equal to 2.40. Furthermore, theordinary extinction coefficient of the cap layer at any wavelength inthe range from 500 nm to 650 nm, preferably in the entire wavelengthrange from 500 nm to 650 nm, is preferably higher than or equal to 0 andlower than or equal to 0.01.

In the case where the light-emitting device 600 emits light having apeak wavelength of λ nm, the above-described ordinary refractive indexand ordinary extinction coefficient with respect to the light of λ nmare preferably within the above-described numerical ranges. Moreover,the ordinary extinction coefficient of the cap layer 155 at a wavelengththat is shorter than the peak wavelength λ nm by 100 nm or more ispreferably higher than 0.01 for a reduced loss due to light absorptionand a higher refractive index at the wavelength λ nm. Furthermore, theordinary extinction coefficient at any wavelength in the range from 370nm to 700 nm is preferably higher than 0.05 for an increased refractiveindex in a visible light region.

Such a cap layer 155 can be obtained by being formed using a materialhaving the above-described properties (such a material is referred to asa high refractive index material in this specification). In other words,a layer containing a material having the above-described properties(also referred to as a high refractive index material) is formed as thecap layer 155.

The high refractive index material preferably has a condensed ringskeleton having four or more rings, preferably five or more ringsbecause larger polarization of a molecule causes a higher refractiveindex. Furthermore, the high refractive index material achieves the highrefractive index by employing an element with a large atomic numberhaving high atomic refraction. In particular, the high refractive indexmaterial preferably contains a sulfur atom.

Moreover, the high refractive index material is preferably an organiccompound having any of a plurality of naphthalene skeletons, a pluralityof dibenzoquinoxaline skeletons, a plurality of benzonaphthofuranskeletons, and a plurality of benzofuropyrimidine skeletons. Note thatthe organic compound preferably further has a carbazole skeleton or anaryl amine skeleton.

Furthermore, an evaporated film preferably has large anisotropy becauselarge anisotropy increases the film density and thus increases therefractive index. In addition, large anisotropy tends to increase theordinary refractive index, and a higher ordinary refractive indeximproves the outcoupling efficiency of s-polarized light more; thus, anevaporated film of the high refractive index material preferably haslarge anisotropy. Specifically, the alignment order parameter S of theevaporated film, which is calculated from the ordinary extinctioncoefficient peak positioned on the longest wavelength side, ispreferably less than or equal to −0.1, further preferably less than orequal to −0.15, and still further preferably less than or equal to −0.2.

Note that the alignment order parameter S is expressed byS=(k_(e)−k_(o))/(k_(e)+2k_(o)), where k_(o) represents an extinctioncoefficient with respect to light perpendicular to the optical axis andk_(e) represents an extinction coefficient with respect to lightparallel to the optical axis. The alignment order parameter S is used asan index indicating the alignment state of a material. The alignmentorder parameter S falls within the range from −0.5 to +1; it is −0.5 inthe case of completely parallel alignment with respect to the substrate,+1 in the case of completely perpendicular alignment with respect to thesubstrate, and 0 in the case of random alignment.

As the above-described high refractive index material, any of thefollowing organic compounds can be used, for example.

The examples include5,5′-diphenyl-2,2′-di-5H-[1]benzothieno[3,2-c]carbazole (abbreviation:BisBTc),3-{4-(triphenylen-2-yl)phenyl}-9-(triphenylen-2-yl)-9H-carbazole(abbreviation: TpPCzTp),3,6-bis[4-(2-naphthyl)phenyl]-9-(2-naphthyl)-9H-carbazole (abbreviation:PNP2βNC),9-[4-(2,2′-binaphthalen-6-yl)phenyl]-3-[4-(2-naphthyl)phenyl]-9H-carbazole(abbreviation: (βN2)PCPβN),2-{4-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline(abbreviation: 2PCCzPDBq-02),N,N-bis[4-(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)phenyl]-4-amino-p-terphenyl(abbreviation: BnfBB1TP),9-[4-(9′-phenyl-3,3′-bi-9H-carbazol-9-yl)phenyl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine(abbreviation: 9pPCCzPNfpr), and4,8-bis[3-(triphenylen-2-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 4,8mTpP2Bfpm).

The material having the above-described properties is extremely suitableas a material included in the cap layer 155.

The low refractive index layer 156 can be formed using a material havinga carrier-transport property whose ordinary refractive index at anywavelength in the range from 455 nm to 465 nm, preferably in the entirewavelength range from 455 nm to 465 nm is higher than or equal to 1.50and lower than or equal to 1.75. Alternatively, the low refractive indexlayer 156 can be formed using a material having a carrier-transportproperty whose ordinary refractive index at any wavelength in the rangefrom 500 nm to 650 nm, preferably in the entire wavelength range from500 nm to 650 nm is higher than or equal to 1.45 and lower than or equalto 1.70. In the case where the low refractive index layer 156 is formedin the electron-transport region, the low refractive index layer 156 isformed as a layer containing a material having an electron-transportproperty. In the case where the low refractive index layer 156 is formedin the hole-transport region, the low refractive index layer 156 isformed as a layer containing a material having a hole-transportproperty.

It is preferable to provide the low refractive index layer 156 in thecarrier-transport region 151, which is a region between thelight-emitting layer 113 and the second electrode 102, because theeffect of improving emission efficiency in this case is larger than thatin the case where a low refractive index layer is provided in thecarrier-transport region 150, which is a region between thelight-emitting layer 113 and the first electrode 101.

Note that the structure where the first electrode 101 is an anode andthe second electrode 102 is a cathode is preferable to increase emissionefficiency of the case where a high refractive index cap layer and a lowrefractive index electron-transport layer are employed. This is becausethe second electrode 102 can be formed using Ag or the like having a lowwork function and reflectivity. In such a case, the carrier-transportregion 150 serves as the hole-transport region, the carrier-transportregion 151 serves as the electron-transport region, and the lowrefractive index layer 156 is provided in the electron-transport region.

In the case where the low refractive index layer 156 is provided in theelectron-transport region, the low refractive index layer 156 is formedas a layer containing a low refractive index material having anelectron-transport property. The following substances can be given asexamples of the low refractive index material having anelectron-transport property and a refractive index in theabove-described range. Note that substances other than those describedbelow can also be used similarly as long as they are substances which afilm with an electron mobility of 1×10⁻⁷ cm²/Vs or higher and arefractive index in the above-described range can be formed of.

As the low refractive index material having an electron-transportproperty, an organic compound which includes at least one six-memberedheteroaromatic ring having 1 to 3 nitrogen atoms, a plurality ofaromatic hydrocarbon rings each of which has 6 to 14 carbon atomsforming a ring and at least two of which are benzene rings, and aplurality of hydrocarbon groups forming a bond by sp³ hybrid orbitalscan be given.

In the above organic compound, carbon atoms forming a bond by sp³ hybridorbitals preferably account for higher than or equal to 10% and lowerthan or equal to 60%, further preferably higher than or equal to 10% andlower than or equal to 50% of total carbon atoms in molecules of theorganic compound. Alternatively, when the above organic compound issubjected to ¹H-NMR measurement, the integral value of signals at lowerthan 4 ppm is preferably ½ or more of the integral value of signals at 4ppm or higher.

The molecular weight of the organic compound having anelectron-transport property is preferably greater than or equal to 500and less than or equal to 2000. It is preferable that all thehydrocarbon groups forming a bond by sp³ hybrid orbitals in the aboveorganic compound be bonded to the aromatic hydrocarbon rings each having6 to 14 carbon atoms forming a ring.

The organic compound having an electron-transport property is preferablyan organic compound represented by General Formula (G_(e1)1) or(G_(e1)1-1).

In the formula, A represents a six-membered heteroaromatic ring having 1to 3 nitrogen atoms, and is preferably any of a pyridine ring, apyrimidine ring, a pyrazine ring, a pyridazine ring, and a triazinering.

Furthermore, R²⁰⁰ represents any of hydrogen, an alkyl group having 1 to6 carbon atoms, an alicyclic group having 3 to 10 carbon atoms, and asubstituent represented by General Formula (G_(e1)1-1).

At least one of R²⁰¹ to R²¹⁵ represents a phenyl group having asubstituent and the others each independently represent any of hydrogen,an alkyl group having 1 to 6 carbon atoms, an alicyclic group having 3to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbongroup having 6 to 14 carbon atoms in a ring, and a substituted orunsubstituted pyridyl group. Note that R²⁰¹, R²⁰³, R²⁰⁵, R²⁰⁶, R²⁰⁸,R²¹⁰, R²¹¹, R²¹³, and R²¹⁵ are preferably hydrogen. The phenyl grouphaving a substituent has one or two substituents, which eachindependently represent any of an alkyl group having 1 to 6 carbonatoms, an alicyclic group having 3 to 10 carbon atoms, and a substitutedor unsubstituted aromatic hydrocarbon group having 6 to 14 carbon atomsin a ring.

The organic compound represented by General Formula (G_(e1)1) has aplurality of hydrocarbon groups selected from an alkyl group having 1 to6 carbon atoms and an alicyclic group having 3 to 10 carbon atoms, andcarbon atoms forming a bond by sp³ hybrid orbitals account for higherthan or equal to 10% and lower than or equal to 60% of total carbonatoms in molecules of the organic compound.

The organic compound having an electron-transport property is preferablyan organic compound represented by General Formula (G_(e1)2).

In the formula, two or three of Q¹ to Q³ represent N; in the case wheretwo of Q¹ to Q³ are N, the rest represents CH.

At least any one of R²⁰¹ to R²¹⁵ represents a phenyl group having asubstituent and the others each independently represent any of hydrogen,an alkyl group having 1 to 6 carbon atoms, an alicyclic group having 3to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbongroup having 6 to 14 carbon atoms in a ring, and a substituted orunsubstituted pyridyl group. Note that R²⁰¹, R²⁰³, R²⁰⁵, R²⁰⁶, R²⁰⁸,R²¹⁰, R²¹, R²¹³, and R²¹⁵ are preferably hydrogen. The phenyl grouphaving a substituent has one or two substituents, which eachindependently represent any of an alkyl group having 1 to 6 carbonatoms, an alicyclic group having 3 to 10 carbon atoms, and a substitutedor unsubstituted aromatic hydrocarbon group having 6 to 14 carbon atomsin a ring.

The organic compound represented by General Formula (G_(e1)2) has aplurality of hydrocarbon groups selected from an alkyl group having 1 to6 carbon atoms and an alicyclic group having 3 to 10 carbon atoms, andcarbon atoms forming a bond by sp³ hybrid orbitals account for higherthan or equal to 10% and lower than or equal to 60% of total carbonatoms in molecules of the organic compound.

In the organic compound represented by General Formula (G_(e1)1) or(G_(e1)2), the phenyl group having a substituent is preferably a grouprepresented by Formula (G_(e1)1-2).

In the formula, α represents a substituted or unsubstituted phenylenegroup and is preferably a meta-substituted phenylene group. In the casewhere the meta-substituted phenylene group has a substituent, thesubstituent is also preferably meta-substituted. The substituent ispreferably an alkyl group having 1 to 6 carbon atoms or an alicyclicgroup having 3 to 10 carbon atoms, further preferably an alkyl grouphaving 1 to 6 carbon atoms, and still further preferably a t-butylgroup.

R²²⁰ represents an alkyl group having 1 to 6 carbon atoms, an alicyclicgroup having 3 to 10 carbon atoms, or a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 14 carbon atoms in a ring.

In addition, j and k each represent 1 or 2. In the case where j is 2, aplurality of a may be the same or different from each other. In the casewhere k is 2, a plurality of R²²⁰ may be the same or different from eachother. R²²⁰ is preferably a phenyl group, further preferably a phenylgroup that has an alkyl group having 1 to 6 carbon atoms or an alicyclicgroup having 3 to 10 carbon atoms at one or both of the twometa-positons. The substituent at one or both of the two meta-positonsof the phenyl group is preferably an alkyl group having 1 to 6 carbonatoms, further preferably a t-butyl group.

Note that in the low refractive index layer 156, a mixed material of theorganic compound and a metal complex of an alkali metal or an alkalineearth metal is preferably used as the low refractive index materialhaving an electron-transport property. A heterocyclic compound having adiazine skeleton, a heterocyclic compound having a triazine skeleton,and a heterocyclic compound having a pyridine skeleton are preferable interms of driving lifetime because they are likely to form an exciplexwith an organometallic complex of an alkali metal with stable energy(the emission wavelength of the exciplex easily becomes longer). Inparticular, the heterocyclic compound having a diazine skeleton or theheterocyclic compound having a triazine skeleton has a deep LUMO leveland thus is preferred for stabilization of energy of an exciplex.

Note that the organometallic complex of an alkali metal is preferably ametal complex of sodium or lithium. Alternatively, the organometalliccomplex of an alkali metal preferably has a ligand having a quinolinolskeleton. Further preferably, the organometallic complex of an alkalimetal is preferably a lithium complex having an 8-quinolinolatostructure or a derivative thereof. The derivative of a lithium complexhaving an 8-quinolinolato structure is preferably a lithium complexhaving an 8-quinolinolato structure having an alkyl group, and furtherpreferably has a methyl group.

It is possible that 8-quinolinolato-lithium having an alkyl group be ametal complex with a low refractive index. Specifically, the ordinaryrefractive index of the metal complex in a thin film state with respectto light with a wavelength in the range from 455 nm to 465 nm can behigher than or equal to 1.45 and lower than or equal to 1.70, and theordinary refractive index thereof with respect to light with awavelength of 633 nm can be higher than or equal to 1.40 and lower thanor equal to 1.65.

Specific examples of the metal complex include8-hydroxyquinolinato-lithium (abbreviation: Liq) and8-hydroxyquinolinato-sodium (abbreviation: Naq). In particular, acomplex of a monovalent metal ion, especially a complex of lithium ispreferable, and Liq is further preferable. Note that in the case wherethe 8-hydroxyquinolinato structure is included, a methyl-substitutedproduct (e.g., a 2-methyl-substituted product, a 5-methyl-substitutedproduct, or 6-methyl-substituted product) thereof is also preferablyused, for example. In particular, the use of an alkali metal complexhaving an 8-quinolinolato structure having an alkyl group at the 6position results in lowering the driving voltage of a light-emittingdevice.

The structure where the first electrode 101 is a cathode and the secondelectrode 102 is an anode may also be employed. In such a case, thecarrier-transport region 150 serves as the electron-transport region,the carrier-transport region 151 serves as the hole-transport region,and the low refractive index layer 156 is provided in the hole-transportregion.

In the case where the low refractive index layer 156 is provided in thehole-transport region, the low refractive index layer 156 is formed as alayer containing a low refractive index material having a hole-transportproperty. The following substances can be given as examples of the lowrefractive index material having a hole-transport property and arefractive index in the above-described range. Note that substancesother than those described below can also be used similarly as long asthey are substances which a film with a hole mobility of 1×10⁻⁷ cm²/Vsor higher and a refractive index in the above-described range can beformed of.

Thus, an example of the low refractive index material having ahole-transport property is a monoamine compound including a firstaromatic group, a second aromatic group, and a third aromatic group, inwhich the first aromatic group, the second aromatic group, and the thirdaromatic group are bonded to the same nitrogen atom.

In the monoamine compound, the proportion of carbon atoms each forming abond by the sp³ hybrid orbitals to the total number of carbon atoms inthe molecule is preferably higher than or equal to 23% and lower than orequal to 55%. In addition, it is preferable that the integral value ofsignals at lower than 4 ppm exceed the integral value of signals at 4ppm or higher in the results of ¹H-NMR measurement conducted on themonoamine compound.

The monoamine compound preferably has at least one fluorene skeleton.One or more of the first aromatic group, the second aromatic group, andthe third aromatic group are preferably a fluorene skeleton. Sincefluorenylamine has an effect of increasing the HOMO level, bonding ofthree fluorenes to nitrogen of the monoamine compound possibly increasesthe HOMO level significantly. In that case, a difference in HOMO levelbetween the monoamine compound and peripheral materials becomes large,which might affect driving voltage, reliability, and the like. Thus, anyone or two of the first to third aromatic groups are further preferablyfluorene skeletons.

Examples of the above-described material include organic compoundshaving structures represented by General Formulae (G_(h1)1) to (G_(h1)4)shown below.

In General Formula (G_(h1)1), Ar¹ and Ar² each independently represent asubstituent with a benzene ring or a substituent in which two or threebenzene rings are bonded to each other. Note that one or both of Ar¹ andAr² have one or more hydrocarbon groups each having 1 to 12 carbon atomseach forming a bond only by the sp³ hybrid orbitals. The total number ofcarbon atoms contained in all of the hydrocarbon groups bonded to Ar¹and Ar² is 8 or more and the total number of carbon atoms contained inall of the hydrocarbon groups bonded to Ar¹ or Ar² is 6 or more. Notethat in the case where a plurality of straight-chain alkyl groups eachhaving one or two carbon atoms are bonded to Ar¹ or Ar² as thehydrocarbon groups, the straight-chain alkyl groups may be bonded toeach other to form a ring.

In General Formula (G_(h1)2), m and r each independently represent 1 or2 and m+r is 2 or 3. Furthermore, t represents an integer of 0 to 4 andis preferably 0. R⁵ represents hydrogen or a hydrocarbon group having 1to 3 carbon atoms. When m is 2, the kind and number of substituents andthe position of bonds included in one phenylene group may be the same asor different from those of the other phenylene group; and when r is 2,the kind and number of substituents and the position of bonds includedin one phenyl group may be the same as or different from those of theother phenyl group. In the case where t is an integer of 2 to 4, R⁵s maybe the same as or different from each other; and adjacent groups(adjacent R⁵s) may be bonded to each other to form a ring.

In General Formulae (G_(h1)2) and (G_(h1)3), n and p each independentlyrepresent 1 or 2 and n+p is 2 or 3. In addition, s represents an integerof 0 to 4 and is preferably 0. R⁴ represents hydrogen or a hydrocarbongroup having 1 to 3 carbon atoms. When n is 2, the kind and number ofsubstituents and the position of bonds in one phenylene group may be thesame as or different from those of the other phenylene group; and when pis 2, the kind and number of substituents and the position of bonds inone phenyl group may be the same as or different from those of the otherphenyl group. In the case where s is an integer of 2 to 4, R⁴s may bethe same as or different from each other.

In General Formulae (G_(h1)2) to (G_(h1)4), R¹⁰ to R¹⁴ and R²⁰ to R²⁴each independently represent hydrogen or a hydrocarbon group having 1 to12 carbon atoms each forming a bond only by the sp³ hybrid orbitals.Note that at least three of R¹⁰ to R¹⁴ and at least three of R²⁰ to R²⁴are preferably hydrogen. As the hydrocarbon group having 1 to 12 carbonatoms each forming a bond only by the sp³ hybrid orbitals, a tert-butylgroup and a cyclohexyl group are preferable. The total number of carbonatoms contained in R¹⁰ to R¹⁴ and R²⁰ to R²⁴ is 8 or more and the totalnumber of carbon atoms contained in either R¹⁰ to R¹⁴ or R²⁰ to R²⁴ is 6or more. Note that adjacent groups of R⁴, R¹⁰ to R¹⁴ and R²⁰ to R²⁴ maybe bonded to each other to form a ring.

In General Formulae (G_(h1)1) to (G_(h1)4), each u independentlyrepresents an integer of 0 to 4 and is preferably 0. Note that in thecase where u is an integer of 2 to 4, R³s may be the same as ordifferent from each other. In addition, R¹, R², and R³ eachindependently represent an alkyl group having 1 to 4 carbon atoms and R¹and R² may be bonded to each other to form a ring.

An arylamine compound that has at least one aromatic group having firstto third benzene rings and at least three alkyl groups can also be givenas the low refractive index material having a hole-transport property.Note that the first to third benzene rings are bonded in this order andthe first benzene ring is directly bonded to nitrogen of amine.

The first benzene ring may further include a substituted orunsubstituted phenyl group and preferably includes an unsubstitutedphenyl group. Furthermore, the second benzene ring or the third benzenering may include a phenyl group substituted by an alkyl group.

Note that hydrogen is not directly bonded to carbon atoms at 1- and3-positions in two or more of, preferably all of the first to thirdbenzene rings, and the carbon atoms are bonded to any of the first tothird benzene rings, the phenyl group substituted by the alkyl group,the at least three alkyl groups, and the nitrogen of the amine.

It is preferable that the arylamine compound further include a secondaromatic group. It is preferable that the second aromatic group have anunsubstituted monocyclic ring or a substituted or unsubstituted bicyclicor tricyclic condensed ring; in particular, it is further preferablethat the second aromatic group be a group having a substituted orunsubstituted bicyclic or tricyclic condensed ring where the number ofcarbon atoms forming the ring is 6 to 13. It is still further preferablethat the second aromatic group be a group including a fluorene ring.Note that a dimethylfluorenyl group is preferable as the second aromaticgroup.

It is preferable that the arylamine compound further include a thirdaromatic group. The third aromatic group is a group having 1 to 3substituted or unsubstituted benzene rings.

It is preferable that the at least three alkyl groups and the alkylgroup substituted for the phenyl group be each a chain alkyl grouphaving 2 to 5 carbon atoms. In particular, as the alkyl group, a chainalkyl group having a branch formed of 3 to 5 carbon atoms is preferable,and a t-butyl group is further preferable.

Examples of the above-described material having a hole-transportproperty include organic compounds having structures represented byGeneral Formulae (G_(h2)1) to (G_(h2)3) shown below.

Note that in General Formula (G_(h2)1), Ar¹′ represents a substituted orunsubstituted benzene ring or a substituent in which two or threesubstituted or unsubstituted benzene rings are bonded to one another.

Note that in General Formula (G_(h2)2), x and y each independentlyrepresent 1 or 2 and x+y is 2 or 3. Furthermore, R¹⁰⁹ represents analkyl group having 1 to 4 carbon atoms, and w represents an integer of 0to 4. R¹⁴¹ to R¹⁴⁵ each independently represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, and a cycloalkyl group having 5to 12 carbon atoms. When w is an integer of 2 or more, R¹⁰⁹s may be thesame as or different from each other. When x is 2, the kind and numberof substituents and the position of bonds included in one phenylenegroup may be the same as or different from those of the other phenylenegroup. When y is 2, the kind and number of substituents and the positionof bonds included in one phenyl group including R¹⁴¹ to R¹⁴⁵ may be thesame as or different from those of the other phenyl group including R¹⁴¹to R¹⁴⁵.

In General Formula (G_(h2)3), R¹⁰¹ to R¹⁰⁵ each independently representany one of hydrogen, an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 6 to 12 carbon atoms, and a substituted orunsubstituted phenyl group.

In General Formulae (G_(h2)1) to (G_(h2)3), R¹⁰⁶, R¹⁰⁷, and R¹⁰⁸ eachindependently represent an alkyl group having 1 to 4 carbon atoms, and vrepresents an integer of 0 to 4. Note that when v is 2 or more, R¹⁰⁸smay be the same as or different from each other. One of R¹¹¹ to R¹¹⁵represents a substituent represented by General Formula (g1), and theothers each independently represent any one of hydrogen, an alkyl grouphaving 1 to 6 carbon atoms, and a substituted or unsubstituted phenylgroup. In General Formula (g1), one of R¹²¹ to R¹²⁵ represents asubstituent represented by General Formula (g2), and the others eachindependently represent any one of hydrogen, an alkyl group having 1 to6 carbon atoms, and a phenyl group substituted by an alkyl group having1 to 6 carbon atoms. In General Formula (g2), R¹³¹ to R¹³⁵ eachindependently represent any one of hydrogen, an alkyl group having 1 to6 carbon atoms, and a phenyl group substituted by an alkyl group having1 to 6 carbon atoms. Note that at least three of R¹¹¹ to R¹¹⁵, R¹²¹ toR¹²⁵, and R¹³¹ to R¹³⁵ are each an alkyl group having 1 to 6 carbonatoms; the number of substituted or unsubstituted phenyl groups in R¹¹to R¹¹⁵ is one or less; and the number of phenyl groups substituted byan alkyl group having 1 to 6 carbon atoms in R¹²¹ to R¹²¹ and R¹³¹ toR¹³⁵ is one or less. In at least two combinations of the threecombinations R¹¹² and R¹¹⁴, R¹²² and R¹²⁴, and R¹³² and R¹³⁴, at leastone R represents any of the substituents other than hydrogen.

Note that the light-emitting device 600 preferably includes a second lowrefractive index layer 157 in the carrier-transport region 150, which isa region between the light-emitting layer 113 and the first electrode101, as illustrated in FIG. 1B. The existence of the second lowrefractive index layer 157 enables the light-emitting device to havehigher emission efficiency. In the case where the carrier-transportregion 150 is the hole-transport region, the second low refractive indexlayer 157 is formed using the low refractive index material having ahole-transport property. In the case where the carrier-transport region150 is the electron-transport region, the second low refractive indexlayer 157 is formed using the low refractive index material having anelectron-transport property.

Here, in blue light-emitting devices using the cap layer 155, a changein blue index (BI) depending on the presence or absence of the lowrefractive index layer 156 and the second low refractive index layer 157with a varying refractive index of the cap layer 155 was calculated.

Note that the blue index (BI) is a value obtained by dividing currentefficiency (cd/A) by chromaticity y, which is calculated with theCIE1931 color system, and is one of the indicators of characteristics ofblue light emission. As the chromaticity y is smaller, the color purityof blue light emission tends to be higher. With high color purity, awide range of blue can be expressed even with a small number ofluminance components; hence, using blue light emission with high colorpurity reduces the luminance needed for expressing blue, leading tolower power consumption. Thus, BI that is based on chromaticity y, whichis one of the indicators of color purity of blue, is suitably used as ameans for showing efficiency of blue light emission. The light-emittingdevice with higher BI can be regarded as a blue light-emitting devicehaving higher efficiency for a display.

The calculation was performed using an organic device simulator (asemiconducting emissive thin film optics simulator: setfos, produced byCybernet Systems Co., Ltd.). A light-emitting region was fixed to thecenter of the light-emitting layer, a light-emitting material wasassumed to have no alignment, and the exciton generation efficiency andthe internal quantum efficiency were assumed to be 100%. Note thatquenching due to the Purcell effect was taken into consideration in thecalculation. The following table shows the stacked structures of thelight-emitting devices used for the calculation and the values ofordinary refractive index and thickness used for the calculation. Asshown in the table, a light-emitting device 02 and a light-emittingdevice 04 have a device structure including the low refractive indexlayer in the carrier-transport region 151, and a light-emitting device03 and the light-emitting device 04 have a device structure includingthe second low refractive index layer in the carrier-transport region150.

TABLE 1 Light-emitting Light-emitting Light-emitting Light-emittingdevice 01 device 02 device 03 device 04 Cap layer sweep Second electrodeTransflective electrode AgMg (15 nm) Electron-transport layer 1.96 1.681.96 1.68 Hole-blocking layer 1.89 (10 nm) Light-emitting layer 1.97 (25nm) Electron-blocking layer 2.00 (10 nm) Hole-transport layer 1.94 1.941.71 1.71 First electrode Transparent electrode ITSO (10 nm) Reflectiveelectrode Ag (100 nm)

As the emission spectrum of the light-emitting devices, a PL spectrum ofa sample was employed; the sample was formed by co-evaporation of9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviation:αN-βNPAnth) and3,10-bis[N-(9-phenyl-9H-carbazol-2-yl)-N-phenylamino]naphtho[2,3-b;6,7-b′]bisbenzofuran(abbreviation: 3,10PCA2Nbf(IV)-02) to a thickness of 50 nm in a weightratio of αN-βNPAnth to 3,10PCA2Nbf(IV)-02 of 1:0.015 on a quartzsubstrate. The emission peak wavelength λ was set to 458 nm.

The thicknesses of the cap layer, the electron-transport layer, and thehole-transport layer were optimized such that the BI in each conditionwas maximized. Note that the thickness of the hole-transport layer wasoptimized such that the hole-transport layer was positioned in thevicinity of ¾λ from the surface on the EL layer side of the reflectiveelectrode, and the thickness of the electron-transport layer wasoptimized such that the electron-transport layer was positioned in thevicinity of ¼λ from the surface on the EL layer side of thetransflective electrode.

FIG. 17A shows the calculation results. FIG. 17B is a graph where the BIwhen the ordinary refractive index of the cap layer is 1.70 is set to 1.

In FIGS. 17A and 17B, the BI is improved in each light-emitting deviceincluding the low refractive index layer and/or the second lowrefractive index layer. In particular, the light-emitting device 02 andthe light-emitting device 04, which include the low refractive indexlayer in the carrier-transport region 151 between the light-emittinglayer 113 and the second electrode 102, show significant improvementrates. In addition, FIG. 17B demonstrates that the light-emitting device02 and the light-emitting device 04 including the low refractive indexlayer in the carrier-transport region 151 have apparently highimprovement rates in BI in a region where the refractive index of thecap layer is high. In other words, a significant effect can be obtainedby the combinational use of the structure provided with the lowrefractive index layer in the carrier-transport region 151 and the caplayer containing the high refractive index material.

Note that the high refractive index material is contained in the caplayer at 80% or more, and the low refractive index material is containedin the low refractive index layer and the second low refractive indexlayer at 80% or more. In the case where the layers are formed of a mixedmaterial containing a plurality of materials, materials having ordinaryrefractive indexes in the predetermined range account for 80% or more intotal in each of the layers.

A layer containing a material with a predetermined ordinary refractiveindex or ordinary extinction coefficient can be read as a layer havingthe predetermined ordinary refractive index or ordinary extinctioncoefficient.

In the case of calculating the refractive index and extinctioncoefficient of a layer formed of a mixed material, they may be directlymeasured or they may be calculated by multiplying the ordinaryrefractive indexes of films that are formed of only the individualmaterials by their respective percentages in the mixed material andsumming up the products. Note that in the case where precise percentagescannot be obtained, a value obtained by dividing each of the ordinaryrefractive indexes by the number of compositional components and summingup the quotients may be used.

Next, examples of other structures and materials of the light-emittingdevice 600 of one embodiment of the present invention will be described.The light-emitting device of one embodiment of the present inventionincludes, as described above, the EL layer 103 including a plurality oflayers between the first electrode 101 and the light-transmitting secondelectrode 102, and the EL layer 103 includes at least the light-emittinglayer 113 containing a light-emitting material and the low refractiveindex layer. The low refractive index layer is preferably positionedbetween the light-emitting layer 113 and the second electrode.

One of the first electrode 101 and the second electrode 102 serves as ananode and the other serves as a cathode. The anode is preferably formedusing any of metals, alloys, and conductive compounds with a high workfunction (specifically, higher than or equal to 4.0 eV), mixturesthereof, and the like. Specific examples include indium oxide-tin oxide(ITO: indium tin oxide), indium oxide-tin oxide containing silicon orsilicon oxide, indium oxide-zinc oxide, and indium oxide containingtungsten oxide and zinc oxide (IWZO). Such conductive metal oxide filmsare usually formed by a sputtering method, but may be formed byapplication of a sol-gel method or the like. In an example of theformation method, indium oxide-zinc oxide is deposited by a sputteringmethod using a target obtained by adding 1 wt % to 20 wt % of zinc oxideto indium oxide. Furthermore, indium oxide containing tungsten oxide andzinc oxide (IWZO) can be deposited by a sputtering method using a targetin which tungsten oxide and zinc oxide are added to indium oxide at 0.5wt % to 5 wt % and 0.1 wt % to 1 wt %, respectively. Alternatively, gold(Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd),nitride of a metal material (e.g., titanium nitride), or the like can beused as a material of the first electrode 101. Graphene can also be usedas a material of the anode. Note that when a composite materialdescribed later is used for a layer that is in contact with the anode inthe EL layer 103 (the layer is typically a hole-injection layer 111), anelectrode material can be selected regardless of the work function.

As a substance of the cathode, any of metals, alloys, and electricallyconductive compounds with a low work function (specifically, lower thanor equal to 3.8 eV), mixtures thereof, and the like is preferably used.Specific examples of such a cathode material include elements belongingto Group 1 and Group 2 of the periodic table, such as alkali metals(e.g., lithium (Li) and cesium (Cs)), magnesium (Mg), calcium (Ca), andstrontium (Sr), alloys containing these elements (e.g., MgAg and AlLi),rare earth metals such as europium (Eu) and ytterbium (Yb), and alloyscontaining these rare earth metals. However, when the electron-injectionlayer is provided between the cathode and the electron-transport layer,any of a variety of conductive materials such as Al, Ag, ITO, or indiumoxide-tin oxide containing silicon or silicon oxide can be used for thecathode regardless of the work function.

Since the second electrode 102 is the light-transmitting electrode inone embodiment of the present invention, a layer having reflectivitywith respect to light emitted by the light-emitting device 600 ispreferably included in the first electrode 101. Stacked layers of thelayer having reflectivity and a layer formed using a light-transmittingmaterial among the materials given above as preferable materials for theanode or cathode may be used as well.

Films of these conductive materials can be formed by a dry process suchas a vacuum evaporation method or a sputtering method, an ink-jetmethod, a spin coating method, or the like. Alternatively, a wet processusing a sol-gel method or a wet process using a paste of a metalmaterial may be employed.

It is preferable that the EL layer 103 have a stacked-layer structure.Except for the above-described light-emitting layer 113, there is noparticular limitation on the stacked-layer structure, and variousfunctional layers such as a hole-injection layer, a hole-transportlayer, an electron-transport layer, an electron-injection layer, acarrier-blocking layer (e.g., a hole-blocking layer and anelectron-blocking layer), an exciton-blocking layer, an intermediatelayer, and a charge-generation layer can be used. It should be notedthat any of the layers or part of any of the layers is a low refractiveindex layer in one embodiment of the present invention. Furthermore,some of the layers may be low refractive index layers.

In this embodiment, a structure in which the hole-injection layer 111, ahole-transport layer 112, the light-emitting layer 113, anelectron-transport layer 114, and an electron-injection layer 115 arestacked from the first electrode 101 (anode) side as illustrated in FIG.1C is described. Although a case where the second electrode 102 is acathode is described as an example in FIG. 1C, the second electrode 102may be an anode. In such a case, the stacking order of the EL layer 103is reversed from that of FIG. 1C, that is, the electron-injection layer115, the electron-transport layer 114, the light-emitting layer 113, thehole-transport layer 112, and the hole-injection layer 111 are stackedfrom the first electrode 101 side.

Note that in FIG. 1C, the carrier-transport region 150 is thehole-transport region and includes the hole-injection layer 111 and thehole-transport layer 112. Other than these, an electron-blocking layeror the like may be included in the hole-transport region. Furthermore,in FIG. 1C, the carrier-transport region 151 is the electron-transportregion and includes the electron-transport layer 114 and theelectron-injection layer 115. Other than these, a hole-blocking layer orthe like may be included in the electron-transport region.

The hole-injection layer 111 is provided in contact with the anode andhas a function of facilitating injection of holes into the EL layer 103.The hole-injection layer can be formed using a phthalocyanine-basedcomplex compound such as phthalocyanine (abbreviation: H₂Pc) or copperphthalocyanine (abbreviation: CuPc), an aromatic amine compound such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB) or4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD), or a high molecular compound such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS).

The hole-injection layer may be formed using a substance having anacceptor property. Examples of the substance having an acceptor propertyinclude an organic compound having an electron-withdrawing group (ahalogen group or a cyano group), such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil,2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation:HAT-CN), 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane(abbreviation: F6-TCNNQ), or2-(7-dicyanomethylene-1,3,4,5,6,8,9,10-octafluoro-7H-pyren-2-ylidene)malononitrile.A compound in which electron-withdrawing groups are bonded to acondensed aromatic ring having a plurality of heteroatoms, such asHAT-CN, is particularly preferable because it is thermally stable. A[3]radialene derivative having an electron-withdrawing group (inparticular, a cyano group or a halogen group such as a fluoro group) hasa very high electron-accepting property and thus is preferable. Specificexamples includeα,α′,α″-1,2,3-cyclopropanetriylidenetris[4-cyano-2,3,5,6-tetrafluorobenzeneacetonitrile],α,α′,α″-1,2,3-cyclopropanetriylidenetris[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)benzeneacetonitrile],andα,α′,α″-1,2,3-cyclopropanetriylidenetris[2,3,4,5,6-pentafluorobenzeneacetonitrile].As the substance having an acceptor property, molybdenum oxide, vanadiumoxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like canalso be used, other than the above-described organic compounds. Thesubstance having an acceptor property can extract electrons from anadjacent hole-transport layer (or hole-transport material) by theapplication of voltage between the electrodes.

The hole-injection layer may be formed using a composite materialcontaining any of the aforementioned materials having an acceptorproperty and a material having a hole-transport property. As thematerial having a hole-transport property that is used in the compositematerial, any of a variety of organic compounds such as aromatic aminecompounds, heteroaromatic compounds, aromatic hydrocarbons, and highmolecular compounds (e.g., oligomers, dendrimers, or polymers) can beused. Note that the material having a hole-transport property that isused in the composite material preferably has a hole mobility of 1×10⁻⁶cm²Vs or higher. The material having a hole-transport property that isused in the composite material is preferably a compound having acondensed aromatic hydrocarbon ring or a π-electron rich heteroaromaticring. As the condensed aromatic hydrocarbon ring, an anthracene ring, anaphthalene ring, or the like is preferable. As the π-electron richheteroaromatic ring, a condensed aromatic ring having at least one of apyrrole skeleton, a furan skeleton, and a thiophene skeleton ispreferable; specifically, a carbazole ring, a dibenzothiophene ring, ora ring in which an aromatic ring or a heteroaromatic ring is furthercondensed to the carbazole ring or the dibenzothiophene ring ispreferable.

The material having a hole-transport property further preferably has anyof a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiopheneskeleton, and an anthracene skeleton. In particular, an aromatic aminehaving a substituent that includes a dibenzofuran ring or adibenzothiophene ring, an aromatic monoamine that includes a naphthalenering, or an aromatic monoamine in which a 9-fluorenyl group is bonded tonitrogen of amine through an arylene group may be used. Note that thematerial having a hole-transport property preferably has anN,N-bis(4-biphenyl)amino group because a light-emitting device having along lifetime can be fabricated. Specific examples of the materialhaving a hole-transport property includeN-(4-biphenyl)-6,N-diphenylbenzo[b]naphtho[1,2-d]furan-8-amine(abbreviation: BnfABP),N,N-bis(4-biphenyl)-6-phenylbenzo[b]naphtho[1,2-d]furan-8-amine(abbreviation: BBABnf),4,4′-bis(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)-4″-phenyltriphenylamine(abbreviation: BnfBB1BP),N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-6-amine (abbreviation:BBABnf(6)), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-8-amine(abbreviation: BBABnf(8)),N,N-bis(4-biphenyl)benzo[b]naphtho[2,3-d]furan-4-amine (abbreviation:BBABnf(II) (4)),N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation:DBfBB1TP), N-[4-(dibenzothiophen-4-yl)phenyl]-N-phenyl-4-biphenylamine(abbreviation: ThBA1BP), 4-(2-naphthyl)-4′,4″-diphenyltriphenylamine(abbreviation: BBAβNB),4-[4-(2-naphthyl)phenyl]-4′,4″-diphenyltriphenylamine (abbreviation:BBAβNBi), 4,4′-diphenyl-4″-(6;1′-binaphthyl-2-yl)triphenylamine(abbreviation: BBAαNβNB),4,4′-diphenyl-4″-(7;1′-binaphthyl-2-yl)triphenylamine (abbreviation:BBAαNβNB-03), 4,4′-diphenyl-4″-(7-phenyl)naphthyl-2-yltriphenylamine(abbreviation: BBAPβNB-03),4,4′-diphenyl-4″-(6;2′-binaphthyl-2-yl)triphenylamine (abbreviation:BBA(βN2)B), 4,4′-diphenyl-4″-(7;2′-binaphthyl-2-yl)triphenylamine(abbreviation: BBA(βN2)B-03),4,4′-diphenyl-4″-(4;2′-binaphthyl-1-yl)triphenylamine (abbreviation:BBAβNαNB), 4,4′-diphenyl-4″-(5;2′-binaphthyl-1-yl)triphenylamine(abbreviation: BBAβNαNB-02),4-(4-biphenylyl)-4′-(2-naphthyl)-4″-phenyltriphenylamine (abbreviation:TPBiAβNB),4-(3-biphenylyl)-4′-[4-(2-naphthyl)phenyl]-4″-phenyltriphenylamine(abbreviation: mTPBiAβNBi),4-(4-biphenylyl)-4′-[4-(2-naphthyl)phenyl]-4″-phenyltriphenylamine(abbreviation: TPBiAβNBi), 4-phenyl-4′-(1-naphthyl)triphenylamine(abbreviation: αNBA1BP), 4,4′-bis(1-naphthyl)triphenylamine(abbreviation: αNBB1BP),4,4′-diphenyl-4″-[4′-(carbazol-9-yl)biphenyl-4-yl]triphenylamine(abbreviation: YGTBi1BP),4′-[4-(3-phenyl-9H-carbazol-9-yl)phenyl]tris(1,1′-biphenyl-4-yl)amine(abbreviation: YGTBi1BP-02),4-[4′-(carbazol-9-yl)biphenyl-4-yl]-4′-(2-naphthyl)-4″-phenyltriphenylamine(abbreviation: YGTBiβNB),N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBNBSF),N,N-bis([1,1′-biphenyl]-4-yl)-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: BBASF),N,N-bis([1,1′-biphenyl]-4-yl)-9,9′-spirobi[9H-fluoren]-4-amine(abbreviation: BBASF(4)),N-(1,1′-biphenyl-2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi[9H-fluoren]-4-amine(abbreviation: oFBiSF),N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)dibenzofuran-4-amine(abbreviation: FrBiF),N-[4-(1-naphthyl)phenyl]-N-[3-(6-phenyldibenzofuran-4-yl)phenyl]-1-naphthylamine(abbreviation: mPDBfBNBN),4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP),4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:mBPAFLP), 4-phenyl-4′-[4-(9-phenylfluoren-9-yl)phenyl]triphenylamine(abbreviation: BPAFLBi),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBASF),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF),N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-4-amine,N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-3-amine,N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-2-amine,andN,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9′-spirobi-9H-fluoren-1-amine.

As the material having a hole-transport property, the following aromaticamine compounds can also be used:N,N′-di(p-tolyl)-N,N-diphenyl-p-phenylenediamine (abbreviation: DTDPPA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD), and1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B).

As the material having a hole-transport property, any of theabove-described low refractive index materials having a hole-transportproperty can be used as well. In this case, the hole-injection layer canbe a low refractive index layer.

Further preferably, the material having a hole-transport property thatis used in the composite material has a relatively deep HOMO levelhigher than or equal to −5.7 eV and lower than or equal to −5.4 eV. Whenthe material having a hole-transport property that is used in thecomposite material has a relatively deep HOMO level, holes can be easilyinjected into the hole-transport layer 112 to easily provide alight-emitting device having a long lifetime. In addition, when thematerial having a hole-transport property that is used in the compositematerial has a relatively deep HOMO level, induction of holes can beinhibited properly so that the light-emitting device can have a longerlifetime.

Note that mixing the above composite material with a fluoride of analkali metal or an alkaline earth metal (the proportion of fluorineatoms in a layer using the mixed material is preferably higher than orequal to 20%) can lower the refractive index of the layer. Also in thiscase, the hole-injection layer can be a low refractive index layer.

The formation of the hole-injection layer 111 can improve thehole-injection property, offering the light-emitting device with a lowdriving voltage.

Among substances having an acceptor property, the organic compoundhaving an acceptor property is easy to use because it is easilydeposited by vapor deposition.

The hole-transport layer 112 is formed using a material having ahole-transport property. The material having a hole-transport propertypreferably has a hole mobility higher than or equal to 1×10⁻⁶ cm²/Vs.The hole-transport layer 112 can be formed of a single layer or aplurality of layers using any of the aforementioned materials having ahole-transport property that can be used in the composite material ofthe hole-injection layer. As the material having a hole-transportproperty, any of the above-described low refractive index materialshaving a hole-transport property can be used as well. In this case, thehole-transport layer can be a low refractive index layer.

An electron-blocking layer may be provided between the hole-transportlayer 112 and the light-emitting layer 113. For the electron-blockinglayer, a substance having a LUMO level higher than a host material ofthe light-emitting layer 113 by 0.25 eV or more among theabove-described materials that can be used as the material having ahole-transport property in the hole-transport layer is preferably used.

The light-emitting layer 113 preferably includes a light-emittingsubstance and a host material. The light-emitting layer 113 mayadditionally include other materials. Alternatively, the light-emittinglayer 113 may be a stack of two layers with different compositions.

As the light-emitting substance, fluorescent substances, phosphorescentsubstances, substances exhibiting thermally activated delayedfluorescence (TADF), or other light-emitting substances may be used.Note that one embodiment of the present invention is more suitably usedin the case where the light-emitting layer 113 is a layer that exhibitsfluorescence, specifically, blue fluorescence.

Examples of the material that can be used as a fluorescent substance inthe light-emitting layer 113 are as follows. Other fluorescentsubstances can also be used.

The examples include5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation:PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine(abbreviation: PAPP2BPy),N,N-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6FLPAPm),N,N-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn),N,N-bis[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N″′,N″′-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM),2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM),N,N-diphenyl-N,N′-(1,6-pyrene-diyl)bis[(6-phenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation:1,6BnfAPrn-03),3,10-bis[N-(9-phenyl-9H-carbazol-2-yl)-N-phenylamino]naphtho[2,3-b;6,7-b′]bisbenzofuran(abbreviation: 3,10PCA2Nbf(IV)-02), and3,10-bis[N-(dibenzofuran-3-yl)-N-phenylamino]naphtho[2,3-b;6,7-b′]bisbenzofuran(abbreviation: 3,10FrA2Nbf(IV)-02). Condensed aromatic diamine compoundstypified by pyrenediamine compounds such as 1,6FLPAPrn, 1,6mMemFLPAPm,and 1,6BnfAPrn-03 are particularly preferable because of their highhole-trapping properties, high emission efficiency, or high reliability.

Examples of the material that can be used when a phosphorescentsubstance is used as the light-emitting substance in the light-emittinglayer 113 are as follows.

The examples include an organometallic iridium complex having a4H-triazole skeleton, such astris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III)(abbreviation: [Ir(mpptz-dmp)₃]),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Mptz)₃]), ortris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(iPrptz-3b)₃]); an organometallic iridium complexhaving a 1H-triazole skeleton, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃]) ortris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Prptz1-Me)₃]); an organometallic iridium complexhaving an imidazole skeleton, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: [Ir(iPrpmi)₃]) ortris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: [Ir(dmpimpt-Me)₃]); and an organometallic iridium complexin which a phenylpyridine derivative having an electron-withdrawinggroup is a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C²′}iridium(III)picolinate (abbreviation: [Ir(CF₃ppy)₂(pic)]), orbis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)acetylacetonate (abbreviation: FIr(acac)). These compounds exhibit bluephosphorescence and have an emission peak in the wavelength range from440 nm to 520 nm.

Other examples include an organometallic iridium complex having apyrimidine skeleton, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(mppm)₃]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₃]),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₂(acac)]),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(nbppm)₂(acac)]),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(mpmppm)₂(acac)]), or(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]); an organometallic iridium complexhaving a pyrazine skeleton, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]) or(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]); an organometallic iridium complexhaving a pyridine skeleton, such astris(2-phenylpyridinato-N,C²′)iridium(III) (abbreviation: [Ir(ppy)₃]),bis(2-phenylpyridinato-N,C²′)iridium(III) acetylacetonate (abbreviation:[Ir(ppy)₂(acac)]), bis(benzo[h]quinolinato)iridium(III) acetylacetonate(abbreviation: [Ir(bzq)₂(acac)]), tris(benzo[h]quinolinato)iridium(III)(abbreviation: [Ir(bzq)₃]), tris(2-phenylquinolinato-N,C²′)iridium(III)(abbreviation: [Ir(pq)₃]), bis(2-phenylquinolinato-N,C²′)iridium(III)acetylacetonate (abbreviation: [Ir(pq)₂(acac)]),[2-d3-methyl-8-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-κC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III)(abbreviation: [Ir(5mppy-d3)₂(mbfpypy-d3)]),[2-(methyl-d3)-8-[4-(1-methylethyl-1-d)-2-pyridinyl-κN]benzofuro[2,3-b]pyridin-7-yl-κC]bis[5-(methyl-d3)-2-[5-(methyl-d3)-2-pyridinyl-κN]phenyl-κC]iridium(III)(abbreviation: Ir(5mtpy-d6)₂(mbfpypy-iPr-d4)),[2-d3-methyl-(2-pyridinyl-κN)benzofuro[2,3-b]pyridine-κC]bis[2-(2-pyridinyl-κN)phenyl-κC]iridium(III)(abbreviation: [Ir(ppy)₂(mbfpypy-d3)]), or[2-(4-methyl-5-phenyl-2-pyridinyl-N)phenyl-κC]bis[2-(2-pyridinyl-N)phenyl-κC]iridium(III)(abbreviation: [Ir(ppy)₂(mdppy)]); and a rare earth metal complex suchas tris(acetylacetonato) (monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen)]). These are mainly compounds that exhibit greenphosphorescence and have an emission peak in the wavelength range from500 nm to 600 nm. Note that organometallic iridium complexes having apyrimidine skeleton have distinctively high reliability or emissionefficiency and thus are particularly preferable.

Other examples include an organometallic iridium complex having apyrimidine skeleton, such as(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: [Ir(5mdppm)₂(dibm)]),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(5mdppm)₂(dpm)]), orbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(d1npm)₂(dpm)]); an organometallic iridium complexhaving a pyrazine skeleton, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]),bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III)(abbreviation: [Ir(tppr)₂(dpm)]), or(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]); an organometallic iridium complexhaving a pyridine skeleton, such astris(1-phenylisoquinolinato-N,C²′)iridium(III) (abbreviation:[Ir(piq)₃]) or bis(1-phenylisoquinolinato-N,C²′)iridium(III)acetylacetonate (abbreviation: [Ir(piq)₂(acac)]); a platinum complexsuch as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II)(abbreviation: PtOEP); and a rare earth metal complex such astris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)]) ortris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: [Eu(TTA)₃(Phen)]). These compounds exhibit redphosphorescence and have an emission peak in the wavelength range from600 nm to 700 nm. Organometallic iridium complexes having a pyrazineskeleton can provide red light emission with favorable chromaticity.

Besides the above phosphorescent compounds, known phosphorescentcompounds may be selected and used.

Examples of the TADF material include a fullerene, a derivative thereof,an acridine, a derivative thereof, and an eosin derivative. Furthermore,a metal-containing porphyrin, such as a porphyrin containing magnesium(Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), orpalladium (Pd), can be given. Examples of the metal-containing porphyrininclude a protoporphyrin-tin fluoride complex (SnF₂(Proto IX)), amesoporphyrin-tin fluoride complex (SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (SnF₂(Hemato IX)), a coproporphyrintetramethyl ester-tin fluoride complex (SnF₂(Copro III-4Me)), anoctaethylporphyrin-tin fluoride complex (SnF₂(OEP)), anetioporphyrin-tin fluoride complex (SnF₂(Etio I)), and anoctaethylporphyrin-platinum chloride complex (PtCl₂OEP), which arerepresented by the following structural formulae.

Alternatively, a heterocyclic compound having one or both of aπ-electron rich heteroaromatic ring and a π-electron deficientheteroaromatic ring that is represented by the following structuralformulae, such as2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(abbreviation: PIC-TRZ),9-(4,6-diphenyl-1,3,5-triazin-2-yl)-9′-phenyl-9H,9′H-3,3′-bicarbazole(abbreviation: PCCzTzn),2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn),2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine(abbreviation: PXZ-TRZ),3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole(abbreviation: PPZ-3TPT),3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation:ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone(abbreviation: DMAC-DPS), or10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (abbreviation:ACRSA) can be used. Such a heterocyclic compound is preferable becauseof having excellent electron-transport and hole-transport propertiesowing to a π-electron rich heteroaromatic ring and a π-electrondeficient heteroaromatic ring. Among skeletons having the π-electrondeficient heteroaromatic ring, a pyridine skeleton, a diazine skeleton(a pyrimidine skeleton, a pyrazine skeleton, and a pyridazine skeleton),and a triazine skeleton are preferred because of their high stabilityand reliability. In particular, a benzofuropyrimidine skeleton, abenzothienopyrimidine skeleton, a benzofuropyrazine skeleton, and abenzothienopyrazine skeleton are preferred because of their highacceptor properties and high reliability. Among skeletons having theπ-electron rich heteroaromatic ring, an acridine skeleton, a phenoxazineskeleton, a phenothiazine skeleton, a furan skeleton, a thiopheneskeleton, and a pyrrole skeleton have high stability and reliability;thus, at least one of these skeletons is preferably included. Adibenzofuran skeleton is preferable as a furan skeleton, and adibenzothiophene skeleton is preferable as a thiophene skeleton. As apyrrole skeleton, an indole skeleton, a carbazole skeleton, anindolocarbazole skeleton, a bicarbazole skeleton, and a3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole skeleton are particularlypreferable. Note that a substance in which the π-electron richheteroaromatic ring is directly bonded to the π-electron deficientheteroaromatic ring is particularly preferred because theelectron-donating property of the π-electron rich heteroaromatic ringand the electron-accepting property of the π-electron deficientheteroaromatic ring are both improved, the energy difference between theS1 level and the T1 level becomes small, and thus thermally activateddelayed fluorescence can be obtained with high efficiency. Note that anaromatic ring to which an electron-withdrawing group such as a cyanogroup is bonded may be used instead of the π-electron deficientheteroaromatic ring. As a π-electron rich skeleton, an aromatic amineskeleton, a phenazine skeleton, or the like can be used. As a π-electrondeficient skeleton, a xanthene skeleton, a thioxanthene dioxideskeleton, an oxadiazole skeleton, a triazole skeleton, an imidazoleskeleton, an anthraquinone skeleton, a skeleton containing boron such asphenylborane or boranthrene, an aromatic ring or a heteroaromatic ringhaving a cyano group or a nitrile group such as benzonitrile orcyanobenzene, a carbonyl skeleton such as benzophenone, a phosphineoxide skeleton, a sulfone skeleton, or the like can be used. Asdescribed above, a π-electron deficient skeleton and a π-electron richskeleton can be used instead of at least one of the π-electron deficientheteroaromatic ring and the π-electron rich heteroaromatic ring.

Alternatively, a TADF material whose singlet excited state and tripletexcited state are in a thermal equilibrium state may be used. Such aTADF material has a short emission lifetime (excitation lifetime), whichallows inhibition of a decrease in efficiency in a high-luminance regionof a light-emitting element. Specifically, a material having thefollowing molecular structure can be used.

Note that a TADF material is a material having a small differencebetween the S1 level and the T1 level and a function of convertingtriplet excitation energy into singlet excitation energy by reverseintersystem crossing. Thus, a TADF material can upconvert tripletexcitation energy into singlet excitation energy (i.e., reverseintersystem crossing) using a small amount of thermal energy andefficiently generate a singlet excited state. In addition, the tripletexcitation energy can be converted into light.

An exciplex whose excited state is formed of two kinds of substances hasan extremely small difference between the S1 level and the T1 level andfunctions as a TADF material capable of converting triplet excitationenergy into singlet excitation energy.

A phosphorescent spectrum observed at a low temperature (e.g., 77 K to10 K) is used for an index of the T1 level. When the level of energywith a wavelength of the line obtained by extrapolating a tangent to thefluorescent spectrum at a tail on the short wavelength side is the S1level and the level of energy with a wavelength of the line obtained byextrapolating a tangent to the phosphorescent spectrum at a tail on theshort wavelength side is the T1 level, the difference between the S1level and the T1 level of the TADF material is preferably smaller thanor equal to 0.3 eV, further preferably smaller than or equal to 0.2 eV.

When a TADF material is used as the light-emitting substance, the S1level of the host material is preferably higher than that of the TADFmaterial. In addition, the T1 level of the host material is preferablyhigher than that of the TADF material.

As the host material in the light-emitting layer, variouscarrier-transport materials such as materials having anelectron-transport property, materials having a hole-transport property,and the TADF materials can be used.

The material having a hole-transport property is preferably an organiccompound having an amine skeleton or a π-electron rich heteroaromaticring skeleton, for example. Examples of the material include a compoundhaving an aromatic amine skeleton, such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N-bis(3-methylphenyl)-N,N-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(i-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF), orN-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9′-spirobi[9H-fluoren]-2-amine(abbreviation: PCBASF); a compound having a carbazole skeleton, such as1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), or3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound havinga thiophene skeleton, such as4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III), or4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV); and a compound having a furan skeleton, suchas 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation:DBF3P-II) or4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II). Among the above materials, the compoundhaving an aromatic amine skeleton and the compound having a carbazoleskeleton are preferable because these compounds are highly reliable andhave high hole-transport properties to contribute to a reduction indriving voltage. In addition, the organic compounds given as examples ofthe material having a hole-transport property that can be used for thehole-transport layer 112 can also be used.

As the material having an electron-transport property, for example, ametal complex such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II)(abbreviation: BeBq2),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), orbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); or anorganic compound having a π-electron deficient heteroaromatic ring ispreferable. Examples of the organic compound having a π-electrondeficient heteroaromatic ring include an organic compound having anazole skeleton, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI),2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II), or 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs); an organic compound having a heteroaromatic ringhaving a pyridine skeleton, such as3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy),1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB),bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation:BCP), or 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline(abbreviation: NBPhen), an organic compound having a diazine skeleton,such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq),2-[4′-(9-phenyl-9H-carbazol-3-yl)-3,1′-biphenyl-1-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mpPCBPDBq),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 6mDBTPDBq-II),9-[(3′-dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine(abbreviation: 9mDBtBPNfpr),9-[3′-dibenzothiophen-4-yl)bipheny-4-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine(abbreviation: 9pmDBtBPNfpr),4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine(abbreviation: 4,6mDBTP2Pm-II),4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation:4,6mCzP2Pm),9,9′-[pyrimidine-4,6-diylbis(biphenyl-3,3′-diyl)]bis(9H-carbazole)(abbreviation: 4,6mCzBP2Pm),8-(1,1′-biphenyl-4-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 8BP-4mDBtPBfpm),3,8-bis[3-(dibenzothiophen-4-yl)phenyl]benzofuro[2,3-b]pyrazine(abbreviation: 3,8mDBtP2Bfpr),4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 4,8mDBtP2Bfpm),8-[3′-(dibenzothiophen-4-yl)(1,1′-biphenyl-3-yl)]naphtho[1′,2′:4,5]furo[3,2-d]pyrimidine(abbreviation: 8mDBtBPNfpm),8-[(2,2′-binaphthalen)-6-yl)]-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 8(βN2)-4mDBtPBfpm),2,2′-(pyridine-2,6-diyl)bis(4-phenylbenzo[h]quinazoline) (abbreviation:2,6(P-Bqn)2Py),2,2′-(pyridine-2,6-diyl)bis{4-[4-(2-naphthyl)phenyl]-6-phenylpyrimidine}(abbreviation: 2,6(NP-PPm)2Py),6-(1,1′-biphenyl-3-yl)-4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenylpyrimidine(abbreviation: 6mBP-4Cz2PPm),2,6-bis(4-naphthalen-1-ylphenyl)-4-[4-(3-pyridyl)phenyl]pyrimidine(abbreviation: 2,4NP-6PyPPm),4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenyl-6-(1,1′-biphenyl-4-yl)pyrimidine(abbreviation: 6BP-4Cz2PPm), or7-[4-(9-phenyl-9H-carbazol-2-yl)quinazolin-2-yl]-7H-dibenzo[c,g]carbazol(abbreviation: PC-cgDBCzQz); and an organic compound having aheteroaromatic ring having a triazine skeleton, such as2-[(1,1′-biphenyl)-4-yl]-4-phenyl-6-[9,9′-spirobi(9H-fluoren)-2-yl]-1,3,5-triazine(abbreviation: BP-SFTzn),2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mBnfBPTzn),2-{3-[3-(benzo[b]naphtho[1,2-d]furan-6-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mBnfBPTzn-02),2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn),9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9′-phenyl-2,3′-bi-9H-carbazole(abbreviation: mPCCzPTzn-02),2-[3′-(9,9-dimethyl-9H-fluoren-2-yl)-1,1′-biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine(abbreviation: mFBPTzn),5-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-7,7-dimethyl-5H,7H-indeno[2,1-b]carbazole(abbreviation: mINc(II)PTzn),2-{3-[3-(dibenzothiophen-4-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mDBtBPTzn),2,4,6-tris[3′-(pyridin-3-yl)biphenyl-3-yl]-1,3,5-triazine (abbreviation:TmPPPyTz),2-[3-(2,6-dimethyl-3-pyridinyl)-5-(9-phenanthrenyl)phenyl]-4,6-diphenyl-1,3,5-triazine(abbreviation: mPn-mDMePyPTzn),11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazin-2-yl]-11,12-dihydro-12-phenylindolo[2,3-a]carbazole(abbreviation: BP-Icz(II)Tzn),2-[3′-(triphenylen-2-yl)-1,1′-biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine(abbreviation: mTpBPTzn),9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-dibenzothiophenyl]-2-phenyl-9H-carbazole(abbreviation: PCDBfTzn), or2-[1,1′-biphenyl]-3-yl-4-phenyl-6-(8-[1,1′:4′,1″-terphenyl]-4-yl-1-dibenzofuranyl)-1,3,5-triazine(abbreviation: mBP-TPDBfTzn). Among the above materials, the organiccompound having a heteroaromatic ring having a diazine skeleton, theorganic compound having a heteroaromatic ring having a pyridineskeleton, and the organic compound having a heteroaromatic ring having atriazine skeleton have high reliability and thus are preferable. Inparticular, the organic compound having a heteroaromatic ring having adiazine (pyrimidine or pyrazine) skeleton and the organic compoundhaving a heteroaromatic ring having a triazine skeleton have a highelectron-transport property to contribute to a reduction in drivingvoltage.

As the TADF material that can be used as the host material, the abovematerials mentioned as the TADF material can also be used. When the TADFmaterial is used as the host material, triplet excitation energygenerated in the TADF material is converted into singlet excitationenergy by reverse intersystem crossing and transferred to thelight-emitting substance, whereby the emission efficiency of thelight-emitting device can be increased. Here, the TADF materialfunctions as an energy donor, and the light-emitting substance functionsas an energy acceptor.

This is very effective in the case where the light-emitting substance isa fluorescent substance. In that case, the S1 level of the TADF materialis preferably higher than that of the fluorescent substance in orderthat high emission efficiency can be achieved. Furthermore, the T1 levelof the TADF material is preferably higher than the S1 level of thefluorescent substance. Therefore, the T1 level of the TADF material ispreferably higher than that of the fluorescent substance.

It is also preferable to use a TADF material that emits light whosewavelength overlaps with the wavelength of a lowest-energy-sideabsorption band of the fluorescent substance, in which case excitationenergy is transferred smoothly from the TADF material to the fluorescentsubstance and light emission can be obtained efficiently.

In addition, in order to efficiently generate singlet excitation energyfrom the triplet excitation energy by reverse intersystem crossing,carrier recombination preferably occurs in the TADF material. It is alsopreferable that the triplet excitation energy generated in the TADFmaterial not be transferred to the triplet excitation energy of thefluorescent substance. For that reason, the fluorescent substancepreferably has a protective group around a luminophore (a skeleton whichcauses light emission) of the fluorescent substance. As the protectivegroup, a substituent having no π bond and a saturated hydrocarbon arepreferably used. Specific examples include an alkyl group having 3 to 10carbon atoms, a substituted or unsubstituted cycloalkyl group having 3to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbonatoms. It is further preferable that the fluorescent substance have aplurality of protective groups. The substituents having no π bond arepoor in carrier transport performance, whereby the TADF material and theluminophore of the fluorescent substance can be made away from eachother with little influence on carrier transportation or carrierrecombination. Here, the luminophore refers to an atomic group(skeleton) that causes light emission in a fluorescent substance. Theluminophore is preferably a skeleton having a π bond, further preferablyincludes an aromatic ring, and still further preferably includes acondensed aromatic ring or a condensed heteroaromatic ring. Examples ofthe condensed aromatic ring or the condensed heteroaromatic ring includea phenanthrene skeleton, a stilbene skeleton, an acridone skeleton, aphenoxazine skeleton, and a phenothiazine skeleton. Specifically, afluorescent substance having any of a naphthalene skeleton, ananthracene skeleton, a fluorene skeleton, a chrysene skeleton, atriphenylene skeleton, a tetracene skeleton, a pyrene skeleton, aperylene skeleton, a coumarin skeleton, a quinacridone skeleton, and anaphthobisbenzofuran skeleton is preferred because of its highfluorescence quantum yield.

In the case where a fluorescent substance is used as the light-emittingsubstance, a material having an anthracene skeleton is suitably used asthe host material. The use of a substance having an anthracene skeletonas the host material for the fluorescent substance makes it possible toobtain a light-emitting layer with high emission efficiency and highdurability. Among the substances having an anthracene skeleton, asubstance having a diphenylanthracene skeleton, in particular, asubstance having a 9,10-diphenylanthracene skeleton, is chemicallystable and thus is preferably used as the host material. The hostmaterial preferably has a carbazole skeleton because the hole-injectionand hole-transport properties are improved; further preferably, the hostmaterial has a benzocarbazole skeleton in which a benzene ring isfurther condensed to carbazole because the HOMO level thereof isshallower than that of carbazole by approximately 0.1 eV and thus holesenter the host material easily. In particular, the host materialpreferably has a dibenzocarbazole skeleton because the HOMO levelthereof is shallower than that of carbazole by approximately 0.1 eV sothat holes enter the host material easily, the hole-transport propertyis improved, and the heat resistance is increased. Accordingly, asubstance that has both a 9,10-diphenylanthracene skeleton and acarbazole skeleton (or a benzocarbazole or dibenzocarbazole skeleton) isfurther preferable as the host material. Note that in terms of thehole-injection and hole-transport properties described above, instead ofa carbazole skeleton, a benzofluorene skeleton or a dibenzofluoreneskeleton may be used. Examples of such a substance include9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA),6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan(abbreviation: 2mBnfPPA),9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene(abbreviation: FLPPA),9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviation:αN-βNPAnth), 9-(1-naphthyl)-10-(2-naphthyl)anthracene (abbreviation:α,β-ADN), 2-(10-phenylanthracen-9-yl)dibenzofuran,2-(10-phenyl-9-anthracenyl)-benzo[b]naphtho[2,3-d]furan (abbreviation:Bnf(II)PhA), 9-(2-naphthyl)-10-[3-(2-naphthyl)phenyl]anthracene(abbreviation: βN-mβNPAnth), and1-[4-(10-[1,1′-biphenyl]-4-yl-9-anthracenyl)phenyl]-2-ethyl-1H-benzimidazole(abbreviation: EtBImPBPhA). In particular, CzPA, cgDBCzPA, 2mBnfPPA, andPCzPA exhibit excellent properties and thus are preferably selected.

Note that the host material may be a mixture of a plurality of kinds ofsubstances; in the case of using a mixed host material, it is preferableto mix a material having an electron-transport property with a materialhaving a hole-transport property. By mixing the material having anelectron-transport property with the material having a hole-transportproperty, the transport property of the light-emitting layer 113 can beeasily adjusted and a recombination region can be easily controlled. Theweight ratio of the content of the material having a hole-transportproperty to the content of the material having an electron-transportproperty may be 1:19 to 19:1.

Note that a phosphorescent substance can be used as part of the mixedmaterial. When a fluorescent substance is used as the light-emittingsubstance, a phosphorescent substance can be used as an energy donor forsupplying excitation energy to the fluorescent substance.

An exciplex may be formed of these mixed materials. These mixedmaterials are preferably selected so as to form an exciplex thatexhibits light emission whose wavelength overlaps with the wavelength ofa lowest-energy-side absorption band of the light-emitting substance, inwhich case energy can be transferred smoothly and light emission can beobtained efficiently. The use of such a structure is preferable becausethe driving voltage can also be reduced.

Note that at least one of the materials forming an exciplex may be aphosphorescent substance. In this case, triplet excitation energy can beefficiently converted into singlet excitation energy by reverseintersystem crossing.

Combination of a material having an electron-transport property and amaterial having a hole-transport property whose HOMO level is higherthan or equal to that of the material having an electron-transportproperty is preferable for forming an exciplex efficiently. In addition,the LUMO level of the material having a hole-transport property ispreferably higher than or equal to that of the material having anelectron-transport property. Note that the LUMO levels and the HOMOlevels of the materials can be derived from the electrochemicalcharacteristics (the reduction potentials and the oxidation potentials)of the materials that are measured by cyclic voltammetry (CV).

The formation of an exciplex can be confirmed by a phenomenon in whichthe emission spectrum of the mixed film in which the material having ahole-transport property and the material having an electron-transportproperty are mixed is shifted to the longer wavelength side than theemission spectrum of each of the materials (or has another peak on thelonger wavelength side) observed by comparison of the emission spectraof the material having a hole-transport property, the material having anelectron-transport property, and the mixed film of these materials, forexample. Alternatively, the formation of an exciplex can be confirmed bya difference in transient response, such as a phenomenon in which thetransient PL lifetime of the mixed film has longer lifetime componentsor has a larger proportion of delayed components than that of each ofthe materials, observed by comparison of transient photoluminescence(PL) of the material having a hole-transport property, the materialhaving an electron-transport property, and the mixed film of thesematerials. The transient PL can be rephrased as transientelectroluminescence (EL). That is, the formation of an exciplex can alsobe confirmed by a difference in transient response observed bycomparison of the transient EL of the material having a hole-transportproperty, the material having an electron-transport property, and themixed film of these materials.

The electron-transport layer 114 is provided between the light-emittinglayer 113 and the cathode and contains a material having anelectron-transport property. The substance having an electron-transportproperty preferably has an electron mobility higher than or equal to1×10⁻⁶ cm²/Vs in the case where the square root of the electric fieldstrength [V/cm] is 600. Note that any other substance can also be usedas long as the substance has an electron-transport property higher thana hole-transport property. An organic compound having a π-electrondeficient heteroaromatic ring is preferable as the above organiccompound. The organic compound having a π-electron deficientheteroaromatic ring is preferably one or more of an organic compoundhaving a heteroaromatic ring having a polyazole skeleton, an organiccompound having a heteroaromatic ring having a pyridine skeleton, anorganic compound having a heteroaromatic ring having a diazine skeleton,and an organic compound having a heteroaromatic ring having a triazineskeleton.

Specific examples of the material having an electron-transport propertythat can be used for the above electron-transport layer include anorganic compound having an azole skeleton, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI),2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II), or 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs); an organic compound having a heteroaromatic ringhaving a pyridine skeleton, such as3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy)1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB),bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation:BCP), or 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline(abbreviation: NBPhen), an organic compound having a diazine skeleton,such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq),2-[4′-(9-phenyl-9H-carbazol-3-yl)-3,1′-biphenyl-1-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mpPCBPDBq),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 6mDBTPDBq-II),9-[(3′-dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine(abbreviation: 9mDBtBPNfpr),9-[3′-dibenzothiophen-4-yl)bipheny-4-yl]naphtho[1′,2′:4,5]furo[2,3-b]pyrazine(abbreviation: 9pmDBtBPNfpr),4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine(abbreviation: 4,6mDBTP2Pm-II),4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation:4,6mCzP2Pm),9,9′-[pyrimidine-4,6-diylbis(biphenyl-3,3′-diyl)]bis(9H-carbazole)(abbreviation: 4,6mCzBP2Pm),8-(1,1′-biphenyl-4-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 8BP-4mDBtPBfpm),3,8-bis[3-(dibenzothiophen-4-yl)phenyl]benzofuro[2,3-b]pyrazine(abbreviation: 3,8mDBtP2Bfpr),4,8-bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 4,8mDBtP2Bfpm),8-[3′-(dibenzothiophen-4-yl)(1,1′-biphenyl-3-yl)]naphtho[1′,2′:4,5]furo[3,2-d]pyrimidine(abbreviation: 8mDBtBPNfpm),8-[(2,2′-binaphthalen)-6-yl)]-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofuro[3,2-d]pyrimidine(abbreviation: 8(βN2)-4mDBtPBfpm),2,2′-(pyridine-2,6-diyl)bis(4-phenylbenzo[h]quinazoline) (abbreviation:2,6(P-Bqn)2Py),2,2′-(pyridine-2,6-diyl)bis{4-[4-(2-naphthyl)phenyl]-6-phenylpyrimidine}(abbreviation: 2,6(NP-PPm)2Py),6-(1,1′-biphenyl-3-yl)-4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenylpyrimidine(abbreviation: 6mBP-4Cz2PPm),2,6-bis(4-naphthalen-1-ylphenyl)-4-[4-(3-pyridyl)phenyl]pyrimidine(abbreviation: 2,4NP-6PyPPm),4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenyl-6-(1,1′-biphenyl-4-yl)pyrimidine(abbreviation: 6BP-4Cz2PPm), or7-[4-(9-phenyl-9H-carbazol-2-yl)quinazolin-2-yl]-7H-dibenzo[c,g]carbazol(abbreviation: PC-cgDBCzQz); and an organic compound having a triazineskeleton, such as2-[(1,1′-biphenyl)-4-yl]-4-phenyl-6-[9,9′-spirobi(9H-fluoren)-2-yl]-1,3,5-triazine(abbreviation: BP-SFTzn),2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mBnfBPTzn),2-{3-[3-(benzo[b]naphtho[1,2-d]furan-6-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mBnfBPTzn-02),2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn),9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9′-phenyl-2,3′-bi-9H-carbazole(abbreviation: mPCCzPTzn-02),2-[3′-(9,9-dimethyl-9H-fluoren-2-yl)-1,1′-biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine(abbreviation: mFBPTzn),5-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-7,7-dimethyl-5H,7H-indeno[2,1-b]carbazole(abbreviation: mINc(II)PTzn),2-{3-[3-(dibenzothiophen-4-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mDBtBPTzn),2,4,6-tris[3′-(pyridin-3-yl)biphenyl-3-yl]-1,3,5-triazine (abbreviation:TmPPPyTz),2-[3-(2,6-dimethyl-3-pyridinyl)-5-(9-phenanthrenyl)phenyl]-4,6-diphenyl-1,3,5-triazine(abbreviation: mPn-mDMePyPTzn),11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazin-2-yl]-11,12-dihydro-12-phenylindolo[2,3-a]carbazole(abbreviation: BP-Icz(II)Tzn),2-[3′-(triphenylen-2-yl)-1,1′-biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine(abbreviation: mTpBPTzn),9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-dibenzothiophenyl]-2-phenyl-9H-carbazole(abbreviation: PCDBfTzn), or2-[1,1′-biphenyl]-3-yl-4-phenyl-6-(8-[1,1′:4′,1″-terphenyl]-4-yl-1-dibenzofuranyl)-1,3,5-triazine(abbreviation: mBP-TPDBfTzn). Among the above materials, the organiccompound having a heteroaromatic ring having a diazine skeleton, theorganic compound having a heteroaromatic ring having a pyridineskeleton, and the organic compound having a heteroaromatic ring having atriazine skeleton have high reliability and thus are preferable. Inparticular, the organic compound having a heteroaromatic ring having adiazine (pyrimidine or pyrazine) skeleton and the organic compoundhaving a heteroaromatic ring having a triazine skeleton have a highelectron-transport property to contribute to a reduction in drivingvoltage.

Note that a mixed material of the material having an electron-transportproperty and a metal complex of an alkali metal or an alkaline earthmetal is preferably used as the electron-transport layer. A heterocycliccompound having a diazine skeleton, a heterocyclic compound having atriazine skeleton, and a heterocyclic compound having a pyridineskeleton are preferable in terms of driving lifetime because they arelikely to form an exciplex with an organometallic complex of an alkalimetal with stable energy (the emission wavelength of the exciplex easilybecomes longer). In particular, the heterocyclic compound having adiazine skeleton or the heterocyclic compound having a triazine skeletonhas a deep LUMO level and thus is preferred for stabilization of energyof an exciplex.

Note that the organometallic complex of an alkali metal is preferably ametal complex of sodium or lithium. Alternatively, the organometalliccomplex of an alkali metal preferably has a ligand having a quinolinolskeleton. Further preferably, the organometallic complex of an alkalimetal is preferably a lithium complex having an 8-quinolinolatostructure or a derivative thereof. The derivative of a lithium complexhaving an 8-quinolinolato structure is preferably a lithium complexhaving an 8-quinolinolato structure having an alkyl group, and furtherpreferably has a methyl group.

Specific examples of the metal complex include8-hydroxyquinolinato-lithium (abbreviation: Liq) and8-hydroxyquinolinato-sodium (abbreviation: Naq). In particular, acomplex of a monovalent metal ion, especially a complex of lithium ispreferable, and Liq is further preferable. Note that in the case wherethe 8-hydroxyquinolinato structure is included, a methyl-substitutedproduct (e.g., a 2-methyl-substituted product, a 5-methyl-substitutedproduct, or 6-methyl-substituted product) thereof is also preferablyused, for example. In particular, the use of an alkali metal complexhaving an 8-quinolinolato structure having an alkyl group at the 6position results in lowering the driving voltage of a light-emittingdevice.

As the material having an electron-transport property, any of theabove-described low refractive index materials having anelectron-transport property can be used as well. In this case, theelectron-transport layer 114 can be a low refractive index layer.

The electron mobility of the electron-transport layer 114 in the casewhere the square root of the electric field strength [V/cm] is 600 ispreferably higher than or equal to 1×10⁻⁷ cm²/Vs and lower than or equalto 5×10⁻⁵ cm²/Vs. The amount of electrons injected into thelight-emitting layer can be controlled by the reduction in theelectron-transport property of the electron-transport layer 114, wherebythe light-emitting layer can be prevented from having excess electrons.It is particularly preferable to employ this structure when thehole-injection layer is formed using a composite material that includesa material having a hole-transport property with a relatively deep HOMOlevel of −5.7 eV or higher and −5.4 eV or lower, in which case a longlifetime can be achieved. In this case, the material having anelectron-transport property preferably has a HOMO level of −6.0 eV orhigher.

A layer including an alkali metal, an alkaline earth metal, a compoundthereof, or a complex thereof such as lithium fluoride (LiF), cesiumfluoride (CsF), calcium fluoride (CaF₂), or 8-hydroxyquinolinato-lithium(Liq) may be provided as the electron-injection layer 115 between theelectron-transport layer 114 and the second electrode 102. For example,an electride or a layer that is formed using a substance having anelectron-transport property and that includes an alkali metal, analkaline earth metal, or a compound thereof can be used as theelectron-injection layer 115. Examples of the electride include asubstance in which electrons are added at high concentration to calciumoxide-aluminum oxide.

Note that as the electron-injection layer 115, it is possible to use alayer including a substance that has an electron-transport property(preferably an organic compound having a bipyridine skeleton) andincludes a fluoride of the alkali metal or the alkaline earth metal at aconcentration higher than that at which the electron-injection layer 115becomes in a microcrystalline state (50 wt % or higher). Since the layerhas a low refractive index, the electron-injection layer can be a lowrefractive index layer; thus, a light-emitting device including thelayer can have high external quantum efficiency.

Instead of the electron-injection layer 115 in FIG. 1C, acharge-generation layer 116 may be provided (FIG. 1D). Thecharge-generation layer 116 refers to a layer capable of injecting holesinto a layer in contact with the cathode side of the charge-generationlayer and electrons into a layer in contact with the anode side thereofwhen a potential is applied. The charge-generation layer 116 includes atleast a p-type layer 117. The p-type layer 117 is preferably formedusing any of the composite materials given above as examples ofmaterials that can be used for the hole-injection layer 111. The p-typelayer 117 may be formed by stacking a film including the above-describedacceptor material as a material included in the composite material and afilm including a hole-transport material. When a potential is applied tothe p-type layer 117, electrons are injected into the electron-transportlayer 114 and holes are injected into the second electrode 102 which isthe cathode; thus, the light-emitting device operates.

Note that the charge-generation layer 116 preferably includes one orboth of an electron-relay layer 118 and an electron-injection bufferlayer 119 in addition to the p-type layer 117.

The electron-relay layer 118 includes at least the substance having anelectron-transport property and has a function of preventing aninteraction between the electron-injection buffer layer 119 and thep-type layer 117 and smoothly transferring electrons. The LUMO level ofthe substance having an electron-transport property included in theelectron-relay layer 118 is preferably between the LUMO level of theacceptor substance in the p-type layer 117 and the LUMO level of asubstance included in a layer of the electron-transport layer 114 thatis in contact with the charge-generation layer 116. As a specific valueof the energy level, the LUMO level of the substance having anelectron-transport property in the electron-relay layer 118 ispreferably higher than or equal to −5.0 eV, further preferably higherthan or equal to −5.0 eV and lower than or equal to −3.0 eV. Note thatas the substance having an electron-transport property in theelectron-relay layer 118, a phthalocyanine-based material or a metalcomplex having a metal-oxygen bond and an aromatic ligand is preferablyused.

The electron-injection buffer layer 119 can be formed using a substancehaving a high electron-injection property, e.g., an alkali metal, analkaline earth metal, a rare earth metal, or a compound thereof (analkali metal compound (including an oxide such as lithium oxide, ahalide, and a carbonate such as lithium carbonate or cesium carbonate),an alkaline earth metal compound (including an oxide, a halide, and acarbonate), or a rare earth metal compound (including an oxide, ahalide, and a carbonate)).

In the case where the electron-injection buffer layer 119 contains thesubstance having an electron-transport property and a donor substance,an organic compound such as tetrathianaphthacene (abbreviation: TTN),nickelocene, or decamethylnickelocene can be used as the donorsubstance, as well as an alkali metal, an alkaline earth metal, a rareearth metal, or a compound thereof (e.g., an alkali metal compound(including an oxide such as lithium oxide, a halide, and a carbonatesuch as lithium carbonate and cesium carbonate), an alkaline earth metalcompound (including an oxide, a halide, and a carbonate), or a rareearth metal compound (including an oxide, a halide, and a carbonate)).

As the substance having an electron-transport property, a materialsimilar to the above-described material for the electron-transport layer114 can be used. Since the above-described material is an organiccompound having a low refractive index, the use of the material for theelectron-injection buffer layer 119 can offer a light-emitting devicewith high external quantum efficiency.

Any of a variety of methods can be used for forming the EL layer 103,regardless of a dry method or a wet method. For example, a vacuumevaporation method, a gravure printing method, an offset printingmethod, a screen printing method, an ink-jet method, a spin coatingmethod, or the like may be used.

Different methods may be used to form the electrodes or the layersdescribed above.

The structure of the layers provided between the first electrode 101 andthe second electrode 102 is not limited to the above-describedstructure. Preferably, a light-emitting region where holes and electronsrecombine is positioned away from the first electrode 101 and the secondelectrode 102 so as to inhibit quenching due to the proximity of thelight-emitting region and a metal used for electrodes orcarrier-injection layers.

Furthermore, in order that transfer of energy from an exciton generatedin the light-emitting layer can be inhibited, preferably, thehole-transport layer or the electron-transport layer, which is incontact with the light-emitting layer 113, particularly acarrier-transport layer closer to the recombination region in thelight-emitting layer 113, is preferably formed using a substance havinga wider band gap than the light-emitting material of the light-emittinglayer or the light-emitting material included in the light-emittinglayer.

Next, an embodiment of a light-emitting device with a structure in whicha plurality of light-emitting units are stacked (this type oflight-emitting device is also referred to as a stacked or tandem device)is described. This light-emitting device includes a plurality oflight-emitting units between an anode and a cathode. One light-emittingunit has substantially the same structure as the EL layer 103illustrated in FIG. 1C. In other words, the light-emitting deviceillustrated in FIG. 1C includes a single light-emitting unit, and thetandem device includes a plurality of light-emitting units.

In the tandem device, a first light-emitting unit and a secondlight-emitting unit are stacked between an anode and a cathode, and acharge-generation layer is provided between the first light-emittingunit and the second light-emitting unit. The first light-emitting unitand the second light-emitting unit may have the same structure ordifferent structures.

The charge-generation layer in the tandem device has a function ofinjecting electrons into one of the light-emitting units and injectingholes into the other of the light-emitting units when voltage is appliedbetween the anode and the cathode. That is, the charge-generation layerinjects electrons into the first light-emitting unit and holes into thesecond light-emitting unit when voltage is applied such that thepotential of the anode becomes higher than the potential of the cathode.

The charge-generation layer preferably has a structure similar to thatof the charge-generation layer 116 described with reference to FIG. 1D.A composite material of an organic compound and a metal oxide has anexcellent carrier-injection property and an excellent carrier-transportproperty; thus, low-voltage driving and low-current driving can beachieved. In the case where the anode-side surface of a light-emittingunit is in contact with the charge-generation layer, thecharge-generation layer can also function as a hole-injection layer ofthe light-emitting unit; therefore, a hole-injection layer is notnecessarily provided in the light-emitting unit.

In the case where the charge-generation layer of the tandem deviceincludes the electron-injection buffer layer 119, the electron-injectionbuffer layer 119 functions as the electron-injection layer in thelight-emitting unit on the anode side; thus, an electron-injection layeris not necessarily formed in the light-emitting unit on the anode side.

The tandem device having two light-emitting units is described above;one embodiment of the present invention can also be applied to a tandemdevice in which three or more light-emitting units are stacked. With aplurality of light-emitting units partitioned by the charge-generationlayer between a pair of electrodes, it is possible to provide along-life device that can emit light with high luminance at a lowcurrent density. A light-emitting apparatus that can be driven at a lowvoltage and has low power consumption can be provided.

When the emission colors of the light-emitting units are different,light emission of a desired color can be obtained from thelight-emitting device as a whole. For example, in a light-emittingdevice having two light-emitting units, the emission colors of the firstlight-emitting unit may be red and green and the emission color of thesecond light-emitting unit may be blue, so that the light-emittingdevice can emit white light as a whole.

The above-described layers or electrodes such as the EL layer 103, thefirst light-emitting unit, the second light-emitting unit, and thecharge-generation layer can be formed by a method such as an evaporationmethod (including a vacuum evaporation method), a droplet dischargemethod (also referred to as an ink-jet method), a coating method, or agravure printing method, for example. A low molecular material, a middlemolecular material (including an oligomer and a dendrimer), or a highmolecular material may be included in the layers or electrodes.

This embodiment can be freely combined with any of the otherembodiments.

Embodiment 2

In this embodiment, a light-emitting apparatus including thelight-emitting device described in Embodiment 1 is described.

In this embodiment, a light-emitting apparatus manufactured using thelight-emitting device described in Embodiment 1 is described withreference to FIGS. 2A and 2B. Note that FIG. 2A is a top view of thelight-emitting apparatus and FIG. 2B is a cross-sectional view takenalong the dashed-dotted lines A-B and C-D in FIG. 2A. Thislight-emitting apparatus includes a driver circuit portion (source linedriver circuit) 601, a pixel portion 602, and a driver circuit portion(gate line driver circuit) 603, which are to control light emission of alight-emitting device and illustrated with dotted lines. Referencenumeral 604 denotes a sealing substrate; 605, a sealing material; and607, a space surrounded by the sealing material 605.

Reference numeral 608 denotes a lead wiring for transmitting signals tobe input to the source line driver circuit 601 and the gate line drivercircuit 603 and receiving signals such as a video signal, a clocksignal, a start signal, and a reset signal from a flexible printedcircuit (FPC) 609 serving as an external input terminal. Although onlythe FPC is illustrated here, a printed wiring board (PWB) may beattached to the FPC. The light-emitting apparatus in the presentspecification includes, in its category, not only the light-emittingapparatus itself but also the light-emitting apparatus provided with theFPC or the PWB.

Next, a cross-sectional structure is described with reference to FIG.2B. The driver circuit portions and the pixel portion are formed over anelement substrate 610; here, the source line driver circuit 601, whichis a driver circuit portion, and one pixel in the pixel portion 602 areillustrated.

The element substrate 610 may be a substrate containing glass, quartz,an organic resin, a metal, an alloy, a semiconductor, or the like or aplastic substrate formed of fiber reinforced plastic (FRP), poly(vinylfluoride) (PVF), polyester, acrylic resin, or the like.

The structure of transistors used in pixels or driver circuits is notparticularly limited. For example, inverted staggered transistors may beused, or staggered transistors may be used. Furthermore, top-gatetransistors or bottom-gate transistors may be used. A semiconductormaterial used for the transistors is not particularly limited, and forexample, silicon, germanium, silicon carbide, gallium nitride, or thelike can be used. Alternatively, an oxide semiconductor containing atleast one of indium, gallium, and zinc, such as an In—Ga—Zn-based metaloxide, may be used.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. A semiconductor having crystallinity ispreferably used because deterioration of the transistor characteristicscan be inhibited.

Here, an oxide semiconductor is preferably used for semiconductordevices such as the transistors provided in the pixels or drivercircuits and transistors used for touch sensors described later, and thelike. In particular, an oxide semiconductor having a wider band gap thansilicon is preferably used. When an oxide semiconductor having a widerband gap than silicon is used, the off-state current of the transistorscan be reduced.

The oxide semiconductor preferably contains at least indium (In) or zinc(Zn). Further preferably, the oxide semiconductor contains an oxiderepresented by an In-M-Zn-based oxide (M represents a metal such as Al,Ti, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf).

As a semiconductor layer, it is particularly preferable to use an oxidesemiconductor film including a plurality of crystal parts whose c-axesare aligned perpendicular to a surface on which the semiconductor layeris formed or the top surface of the semiconductor layer and in which theadjacent crystal parts have no grain boundary.

The use of such materials for the semiconductor layer makes it possibleto provide a highly reliable transistor in which a change in theelectrical characteristics is inhibited.

Charge accumulated in a capacitor through a transistor including theabove-described semiconductor layer can be held for a long time becauseof the low off-state current of the transistor. When such a transistoris used in a pixel, operation of a driver circuit can be stopped while agray scale of an image displayed in each display region is maintained.As a result, an electronic device with extremely low power consumptioncan be obtained.

For stable characteristics of the transistor, a base film is preferablyprovided. The base film can be formed with a single layer or stackedlayers using an inorganic insulating film such as a silicon oxide film,a silicon nitride film, a silicon oxynitride film, or a silicon nitrideoxide film. The base film can be formed by a sputtering method, achemical vapor deposition (CVD) method (e.g., a plasma CVD method, athermal CVD method, or a metal organic CVD (MOCVD) method), an atomiclayer deposition (ALD) method, a coating method, a printing method, orthe like. Note that the base film is not necessarily provided.

Note that an FET 623 is illustrated as a transistor formed in the drivercircuit portion 601. The driver circuit may be formed with any of avariety of circuits such as a CMOS circuit, a PMOS circuit, or an NMOScircuit. Although a driver integrated type in which the driver circuitis formed over the substrate is illustrated in this embodiment, thedriver circuit is not necessarily formed over the substrate, and thedriver circuit can be formed outside, not over the substrate.

The pixel portion 602 includes a plurality of pixels including aswitching FET 611, a current controlling FET 612, and a first electrode613 electrically connected to a drain of the current controlling FET612. One embodiment of the present invention is not limited to thestructure. The pixel portion 602 may include three or more FETs and acapacitor in combination.

Note that an insulator 614 is formed to cover an end portion of thefirst electrode 613. Here, the insulator 614 can be formed using apositive photosensitive acrylic resin film.

In order to improve the coverage with an EL layer or the like which isformed later, the insulator 614 is formed to have a curved surface withcurvature at its upper or lower end portion. For example, in the casewhere a positive photosensitive acrylic resin is used as a material ofthe insulator 614, only the upper end portion of the insulator 614preferably has a curved surface with a curvature radius (0.2 μm to 3μm). As the insulator 614, either a negative photosensitive resin or apositive photosensitive resin can be used.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. Here, the first electrode 613 serves as an anode. Amaterial having a high work function is preferably used as a material ofthe anode. For example, a single-layer film of an ITO film, an indiumtin oxide film containing silicon, an indium oxide film containing zincoxide at 2 wt % to 20 wt %, a titanium nitride film, a chromium film, atungsten film, a Zn film, a Pt film, or the like, a stack of any ofthese films and a film containing silver as its main component, a stackof a titanium nitride film and a film containing aluminum as its maincomponent, a stack of three layers of a titanium nitride film, a filmcontaining aluminum as its main component, and a titanium nitride film,or the like can be used. The stacked-layer structure enables low wiringresistance, favorable ohmic contact, and a function as an anode.

The EL layer 616 is formed by any of a variety of methods such as anevaporation method using an evaporation mask, an inkjet method, and aspin coating method. The EL layer 616 has the structure described inEmbodiment 1.

As a material used for the second electrode 617, which is formed overthe EL layer 616, a material having a low work function (e.g., Al, Mg,Li, and Ca, or an alloy or a compound thereof, such as MgAg, MgIn, andAlLi) is preferably used. In the case where light generated in the ELlayer 616 passes through the second electrode 617, a stack of a thinmetal or alloy film and a transparent conductive film (e.g., ITO, indiumoxide containing zinc oxide at 2 wt % to 20 wt %, indium tin oxidecontaining silicon, or zinc oxide (ZnO)) is preferably used for thesecond electrode 617.

Note that the light-emitting device is formed with the first electrode613, the EL layer 616, and the second electrode 617. The light-emittingdevice is the light-emitting device described in Embodiment 1. In thelight-emitting apparatus of this embodiment, the pixel portion, whichincludes a plurality of light-emitting devices, may include both thelight-emitting device described in Embodiment 1 and a light-emittingdevice having a different structure. In that case, in the light-emittingapparatus of one embodiment of the present invention, a commonhole-transport layer can be used for light-emitting devices that emitlight with different wavelengths, allowing the light-emitting apparatusto be manufactured in a simple process at low costs.

The sealing substrate 604 is attached to the element substrate 610 withthe sealing material 605, so that a light-emitting device 618 isprovided in the space 607 surrounded by the element substrate 610, thesealing substrate 604, and the sealing material 605. The space 607 maybe filled with a filler, or may be filled with an inert gas (such asnitrogen or argon), or the sealing material. It is preferable that thesealing substrate be provided with a recessed portion and a drying agentbe provided in the recessed portion, in which case deterioration due toinfluence of moisture can be inhibited.

An epoxy-based resin or glass frit is preferably used for the sealingmaterial 605. It is preferable that such a material transmit moisture oroxygen as little as possible. As the sealing substrate 604, a glasssubstrate, a quartz substrate, or a plastic substrate formed of fiberreinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylicresin, or the like can be used.

Although not illustrated in FIGS. 2A and 2B, a protective film may beprovided over the cathode. As the protective film, an organic resin filmor an inorganic insulating film may be formed. The protective film maybe formed so as to cover an exposed portion of the sealing material 605.The protective film may be provided so as to cover surfaces and sidesurfaces of the pair of substrates and exposed side surfaces of asealing layer, an insulating layer, and the like.

The protective film can be formed using a material that does not easilytransmit an impurity such as water. Thus, diffusion of an impurity suchas water from the outside into the inside can be effectively inhibited.

As a material of the protective film, an oxide, a nitride, a fluoride, asulfide, a ternary compound, a metal, a polymer, or the like can beused. For example, the material may contain aluminum oxide, hafniumoxide, hafnium silicate, lanthanum oxide, silicon oxide, strontiumtitanate, tantalum oxide, titanium oxide, zinc oxide, niobium oxide,zirconium oxide, tin oxide, yttrium oxide, cerium oxide, scandium oxide,erbium oxide, vanadium oxide, indium oxide, aluminum nitride, hafniumnitride, silicon nitride, tantalum nitride, titanium nitride, niobiumnitride, molybdenum nitride, zirconium nitride, gallium nitride, anitride containing titanium and aluminum, an oxide containing titaniumand aluminum, an oxide containing aluminum and zinc, a sulfidecontaining manganese and zinc, a sulfide containing cerium andstrontium, an oxide containing erbium and aluminum, an oxide containingyttrium and zirconium, or the like.

The protective film is preferably formed using a deposition method withfavorable step coverage. One such method is an atomic layer deposition(ALD) method. A material that can be deposited by an ALD method ispreferably used for the protective film. A dense protective film havingreduced defects such as cracks or pinholes or a uniform thickness can beformed by an ALD method. Furthermore, damage caused to a process memberin forming the protective film can be reduced.

By an ALD method, a uniform protective film with few defects can beformed even on, for example, a surface with a complex uneven shape orupper, side, and lower surfaces of a touch panel.

As described above, the light-emitting apparatus manufactured using thelight-emitting device described in Embodiment 1 can be obtained.

The light-emitting apparatus in this embodiment is manufactured usingthe light-emitting device described in Embodiment 1 and thus can havefavorable characteristics. Specifically, since the light-emitting devicedescribed in Embodiment 1 has high emission efficiency, thelight-emitting apparatus can achieve low power consumption.

FIGS. 3A and 3B each illustrate an example of a light-emitting apparatusthat includes coloring layers (color filters) and the like to improvecolor purity. FIG. 3A illustrates a substrate 1001, a base insulatingfilm 1002, a gate insulating film 1003, gate electrodes 1006, 1007, and1008, a first interlayer insulating film 1020, a second interlayerinsulating film 1021, a peripheral portion 1042, a pixel portion 1040, adriver circuit portion 1041, first electrodes 1024R, 1024G, and 1024B oflight-emitting devices, a partition 1025, an EL layer 1028, a secondelectrode 1029 of the light-emitting devices, a sealing substrate 1031,a sealing material 1032, and the like.

In FIG. 3A, coloring layers (a red coloring layer 1034R, a greencoloring layer 1034G, and a blue coloring layer 1034B) are provided on atransparent base material 1033. A black matrix 1035 may be additionallyprovided. The transparent base material 1033 provided with the coloringlayers and the black matrix is aligned and fixed to the substrate 1001.Note that the coloring layers and the black matrix 1035 are covered withan overcoat layer 1036.

FIG. 3B shows an example in which the coloring layers (the red coloringlayer 1034R, the green coloring layer 1034G, and the blue coloring layer1034B) are provided between the gate insulating film 1003 and the firstinterlayer insulating film 1020. As in the structure, the coloringlayers may be provided between the substrate 1001 and the sealingsubstrate 1031.

The above-described light-emitting apparatus has a structure in whichlight is extracted from the substrate 1001 side where FETs are formed (abottom emission structure), but may have a structure in which light isextracted from the sealing substrate 1031 side (atop emissionstructure). FIG. 4 is a cross-sectional view of a light-emittingapparatus having atop emission structure. In this case, a substrate thatdoes not transmit light can be used as the substrate 1001. The processup to the step of forming a connection electrode which connects the FETand the anode of the light-emitting device is performed in a mannersimilar to that of the light-emitting apparatus having a bottom emissionstructure. Then, a third interlayer insulating film 1037 is formed tocover the electrode 1022. This insulating film may have a planarizationfunction. The third interlayer insulating film 1037 can be formed usinga material similar to that of the second interlayer insulating film1021, and can alternatively be formed using any of other knownmaterials.

The first electrodes 1024R, 1024G, and 1024B of the light-emittingdevices each serve as an anode here, but may serve as a cathode.Furthermore, in the case of a light-emitting apparatus having a topemission structure as illustrated in FIG. 4, the anodes are preferablyreflective electrodes. The EL layer 1028 is formed to have a structuresimilar to the structure of the EL layer 103 described in Embodiment 1.

In the case of a top emission structure as illustrated in FIG. 4,sealing can be performed with the sealing substrate 1031 on which thecoloring layers (the red coloring layer 1034R, the green coloring layer1034G, and the blue coloring layer 1034B) are provided. The sealingsubstrate 1031 may be provided with the black matrix 1035 which ispositioned between pixels. The coloring layers (the red coloring layer1034R, the green coloring layer 1034G, and the blue coloring layer1034B) or the black matrix 1035 may be covered with the overcoat layer1036. Note that a light-transmitting substrate is used as the sealingsubstrate 1031.

In the light-emitting apparatus having a top emission structure, amicrocavity structure can be favorably employed. A light-emitting devicewith a microcavity structure is formed with the use of an electrodeincluding a reflective electrode as one of the electrodes and atransflective electrode as the other electrode. At least an EL layer ispositioned between the reflective electrode and the transflectiveelectrode, and the EL layer includes at least a light-emitting layerserving as a light-emitting region.

Note that the reflective electrode has a visible light reflectivity of40% to 100%, preferably 70% to 100%, and a resistivity of 1×10⁻² Ωcm orlower. In addition, the transflective electrode has a visible lightreflectivity of 20% to 80%, preferably 40% to 70%, and a resistivity of1×10⁻² Ωcm or lower.

Light emitted from the light-emitting layer included in the EL layer isreflected and resonated by the reflective electrode and thetransflective electrode.

In the light-emitting device, by changing thicknesses of the transparentconductive film, the composite material, the carrier-transport material,or the like, the optical path length between the reflective electrodeand the transflective electrode can be changed. Thus, light with awavelength that is resonated between the reflective electrode and thetransflective electrode can be intensified while light with a wavelengththat is not resonated therebetween can be attenuated.

Note that light that is reflected back by the reflective electrode(first reflected light) considerably interferes with light that directlyenters the transflective electrode from the light-emitting layer (firstincident light). For this reason, the optical path length between thereflective electrode and the light-emitting layer is preferably adjustedto (2n−1)λ/4 (n is a natural number of 1 or larger and λ is a wavelengthof light to be amplified). By adjusting the optical path length, thephases of the first reflected light and the first incident light can bealigned with each other and the light emitted from the light-emittinglayer can be further amplified.

Note that in the above structure, the EL layer may include a pluralityof light-emitting layers or may include a single light-emitting layer.The tandem light-emitting device described above may be combined with aplurality of EL layers; for example, a light-emitting device may have astructure in which a plurality of EL layers are provided with acharge-generation layer provided therebetween, and each EL layerincludes a plurality of light-emitting layers or a single light-emittinglayer.

With the microcavity structure, emission intensity with a specificwavelength in the front direction can be increased, whereby powerconsumption can be reduced. Note that in the case of a light-emittingapparatus that displays images with subpixels of four colors, red,yellow, green, and blue, the light-emitting apparatus can have favorablecharacteristics because the luminance can be increased owing to yellowlight emission and each subpixel can employ a microcavity structuresuitable for wavelengths of the corresponding color.

The light-emitting apparatus in this embodiment is manufactured usingthe light-emitting device described in Embodiment 1 and thus can havefavorable characteristics. Specifically, since the light-emitting devicedescribed in Embodiment 1 has high emission efficiency, thelight-emitting apparatus can achieve low power consumption.

The active matrix light-emitting apparatus is described above, whereas apassive matrix light-emitting apparatus is described below. FIGS. 5A and5B illustrate a passive matrix light-emitting apparatus manufacturedusing the present invention. Note that FIG. 5A is a perspective view ofthe light-emitting apparatus, and FIG. 5B is a cross-sectional viewtaken along the line X-Y in FIG. 5A. In FIGS. 5A and 5B, over asubstrate 951, an EL layer 955 is provided between an electrode 952 andan electrode 956. An end portion of the electrode 952 is covered with aninsulating layer 953. A partition layer 954 is provided over theinsulating layer 953. The sidewalls of the partition layer 954 areaslope such that the distance between both sidewalls is graduallynarrowed toward the surface of the substrate. In other words, a crosssection taken along the direction of the short side of the partitionlayer 954 is trapezoidal, and the lower side (a side of the trapezoidthat is parallel to the surface of the insulating layer 953 and is incontact with the insulating layer 953) is shorter than the upper side (aside of the trapezoid that is parallel to the surface of the insulatinglayer 953 and is not in contact with the insulating layer 953). Thepartition layer 954 thus provided can prevent defects in thelight-emitting device due to static electricity or others. The passivematrix light-emitting apparatus also includes the light-emitting devicedescribed in Embodiment 1; thus, the light-emitting apparatus can havehigh reliability or low power consumption.

In the light-emitting apparatus described above, many minutelight-emitting devices arranged in a matrix can each be controlled;thus, the light-emitting apparatus can be suitably used as a displaydevice for displaying images.

This embodiment can be freely combined with any of the otherembodiments.

Embodiment 3 [Light-Emitting Apparatus]

Another example of the light-emitting apparatus of one embodiment of thepresent invention using the above-described light-emitting device and amanufacturing method thereof are described below.

In this specification and the like, a device fabricated using a metalmask or a fine metal mask (FMM, a high-resolution metal mask) isreferred to as a device having a metal mask (MM) structure in somecases. In this specification and the like, a device formed without usinga metal mask or an FMM is referred to as a device having a metalmaskless (MML) structure in some cases.

In this specification and the like, a structure in which light-emittinglayers in light-emitting devices of different colors (here, blue (B),green (G), and red (R)) are separately formed or separately patternedmay be referred to as a side-by-side (SBS) structure. In thisspecification and the like, a light-emitting device capable of emittingwhite light may be referred to as a white light-emitting device. Notethat white light-emitting devices that are combined with coloring layers(e.g., color filters) can be a light-emitting apparatus of full-colordisplay.

Structures of light-emitting devices can be classified roughly into asingle structure and a tandem structure. A light-emitting device havinga single structure includes one light-emitting unit between a pair ofelectrodes, and the light-emitting unit preferably includes one or morelight-emitting layers. To obtain white light emission, two or morelight-emitting layers are selected such that emission colors of thelight-emitting layers are complementary colors. For example, whenemission colors of a first light-emitting layer and a secondlight-emitting layer are complementary colors, the light-emitting devicecan be configured to emit white light as a whole. The same applies to alight-emitting device including three or more light-emitting layers.

A light-emitting device having a tandem structure includes two or morelight-emitting units between a pair of electrode, and eachlight-emitting unit preferably includes one or more light-emittinglayers. To obtain white light emission, the structure is made so thatthe combination of light from light-emitting layers of the plurality oflight-emitting units forms white light. Note that a structure forobtaining white light emission is similar to that in the case of asingle structure. In the light-emitting device having a tandemstructure, it is preferable that an intermediate layer such as acharge-generation layer be provided between the plurality oflight-emitting units.

When the white light-emitting device (having a single structure or atandem structure) and a light-emitting device having an SBS structureare compared to each other, the latter can have lower power consumptionthan the former. To reduce power consumption, a light-emitting devicehaving an SBS structure is preferably used. Meanwhile, thewhite-light-emitting device is preferable in terms of lowermanufacturing cost or higher manufacturing yield because themanufacturing process of the white-light-emitting device is simpler thanthat of a light-emitting device having an SBS structure.

FIG. 14A illustrates a schematic top view of a light-emitting apparatus500 of one embodiment of the present invention. The light-emittingapparatus 500 includes a plurality of light-emitting devices 110Remitting red light, a plurality of light-emitting devices 110G emittinggreen light, and a plurality of light-emitting devices 110B emittingblue light. In FIG. 14A, light-emitting regions of the light-emittingdevices are denoted by R, G, and B to easily differentiate thelight-emitting devices.

The light-emitting devices 110R, the light-emitting devices 110G, andthe light-emitting devices 110B are arranged in a matrix. FIG. 14A showswhat is called a stripe arrangement, in which the light-emitting devicesof the same color are arranged in one direction. Note that thearrangement of the light-emitting devices is not limited thereto;another arrangement such as a delta, zigzag, or PenTile pattern may alsobe used.

The light-emitting device 110R, the light-emitting device 110G, and thelight-emitting device 1101B are arranged in the X direction. Thelight-emitting devices of the same color are arranged in the Y directionintersecting with the X direction.

The light-emitting device 110R, the light-emitting device 110G, and thelight-emitting device 110B have the above structure.

FIG. 14B is a cross-sectional schematic view taken along thedashed-dotted line A1-A2 in FIG. 14A. FIG. 14C is a cross-sectionalschematic view taken along the dashed-dotted line B1-B2 in FIG. 14A.

FIG. 14B shows cross sections of the light-emitting device 110R, thelight-emitting device 110G, and the light-emitting device 1101B. Thelight-emitting device 110R includes a first electrode 101R, an EL layer120R, an EL layer 121, and the second electrode 102. The light-emittingdevice 110G includes a first electrode 101G, an EL layer 120G, the ELlayer (electron-injection layer) 115, and the second electrode 102. Thelight-emitting device 110B includes a first electrode 101B, an EL layer120B, the EL layer 121, and the second electrode 102. The EL layer 121and the second electrode 102 are provided in common to thelight-emitting device 110R, the light-emitting device 110G, and thelight-emitting device 1101B. The EL layer 121 can also be referred to asa common layer.

The EL layer 120R included in the light-emitting device 110R contains alight-emitting organic compound that emits light with intensity at leastin a red wavelength range. The EL layer 120G included in thelight-emitting device 110G contains a light-emitting organic compoundthat emits light with intensity at least in a green wavelength range.The EL layer 120B included in the light-emitting device 1101B contains alight-emitting organic compound that emits light with intensity at leastin a blue wavelength range. At least one of the light-emitting device110R, the light-emitting device 110G, and the light-emitting device1101B is preferably the light-emitting device of one embodiment of thepresent invention, and the light-emitting device of one embodiment ofthe present invention is preferably the light-emitting device 110B.

Each of the EL layer 120R, the EL layer 120G, and the EL layer 120Bincludes at least a light-emitting layer and a hole-transport layer, andmay further include one or more of an electron-injection layer, anelectron-transport layer, a hole-injection layer, a carrier-blockinglayer, an exciton-blocking layer, and the like. The EL layer 121 doesnot necessarily include the light-emitting layer. The EL layer 121 ispreferably the electron-injection layer. In the case where theelectron-transport layer also serves as the electron-injection layer,the EL layer 121 may be omitted.

The first electrode 101R, the first electrode 101G, and the firstelectrode 101B are provided for the respective light-emitting devices.The second electrode 102 and the EL layer 121 are each provided as alayer common to the light-emitting devices. The hole-transport layers inthe EL layers 120, which are separated between the light-emittingdevices with different emission colors, preferably have the samestructure.

A conductive film that transmits visible light is used for either thefirst electrode 101 or the second electrode 102, and a reflectiveconductive film is used for the other. When the first electrode 101 isalight-transmitting electrode and the second electrode 102 is areflective electrode, a bottom-emission display device is obtained. Whenthe first electrode 101 is a reflective electrode and the secondelectrode 102 is a light-transmitting electrode, a top-emission displaydevice is obtained. Note that when both the first electrode 101 and thesecond electrode 102 transmit light, a dual-emission display device canbe obtained. The light-emitting device of one embodiment of the presentinvention is suitable for a top-emission light-emitting device.

An insulating layer 124 is provided to cover end portions of the firstelectrode 101R, the first electrode 101G, and the first electrode 101B.The end portions of the insulating layer 124 are preferably tapered.Note that the insulating layer 124 is not necessarily provided.

The EL layer 120R, the EL layer 120G, and the EL layer 120B each includea region in contact with a top surface of a pixel electrode and a regionin contact with a surface of the insulating layer 124. End portions ofthe EL layer 120R, the EL layer 120G, and the EL layer 120B arepositioned over the insulating layer 124.

As shown in FIG. 14B, there is a gap between the EL layers of twolight-emitting devices with different colors. The EL layer 120R, the ELlayer 120G, and the EL layer 120B are thus preferably provided so as notto be in contact with each other. This effectively preventsunintentional light emission from being caused by current flowingthrough two adjacent EL layers. As a result, the contrast can beincreased to achieve a display device with high display quality.

FIG. 14C shows an example in which the EL layer 120R is formed in a bandshape so as to be continuous in the Y direction. When the EL layer 120Rand the like are formed in a band shape, no space for dividing the layeris needed to reduce a non-light-emitting area between the light-emittingdevices, resulting in a higher aperture ratio. FIG. 14C shows the crosssection of the light-emitting device 110R as an example; thelight-emitting device 110G and the light-emitting device 110B can have asimilar shape. Note that the EL layer may be divided for thelight-emitting devices in the Y direction.

A protective layer 131 is provided over the second electrode 102 so asto cover the light-emitting device 110R, the light-emitting device 110G,and the light-emitting device 110B. The protective layer 131 has afunction of preventing diffusion of impurities such as water into eachlight-emitting device from the above.

The protective layer 131 can have, for example, a single-layer structureor a stacked-layer structure at least including an inorganic insulatingfilm. Examples of the inorganic insulating film include an oxide film ora nitride film such as a silicon oxide film, a silicon oxynitride film,a silicon nitride oxide film, a silicon nitride film, an aluminum oxidefilm, an aluminum oxynitride film, or a hafnium oxide film.Alternatively, a semiconductor material such as indium gallium oxide orindium gallium zinc oxide may be used for the protective layer 131.

As the protective layer 131, a stacked film of an inorganic insulatingfilm and an organic insulating film can be used. For example, astructure in which an organic insulating film is sandwiched between apair of inorganic insulating films is preferable. Furthermore, it ispreferable that the organic insulating film function as a planarizationfilm. With this structure, the top surface of the organic insulatingfilm can be flat, and accordingly, coverage with the inorganicinsulating film over the organic insulating film is improved, leading toan improvement in barrier properties. Moreover, since the top surface ofthe protective layer 131 is flat, in the case where a component (e.g., acolor filter, an electrode of a touch sensor, a lens array, or the like)is provided above the protective layer 131, the component is lessaffected by an uneven shape caused by the lower structure, which ispreferable.

FIG. 14A also illustrates a connection electrode 101C that iselectrically connected to the second electrode 102. The connectionelectrode 101C is supplied with a potential (e.g., an anode potential ora cathode potential) that is to be supplied to the second electrode 102.The connection electrode 101C is provided outside a display region wherethe light-emitting devices 110R and the like are arranged. In FIG. 14A,the second electrode 102 is denoted by a dashed line.

The connection electrode 101C can be provided along the outer peripheryof the display region. For example, the connection electrode 101C may beprovided along one side of the outer periphery of the display region ortwo or more sides of the outer periphery of the display region. That is,in the case where the display region has a rectangular top surface, thetop surface of the connection electrode 101C can have a band shape, an Lshape, a square bracket shape, a quadrangular shape, or the like.

FIG. 14D is a cross-sectional schematic view taken along thedashed-dotted line C1-C2 in FIG. 14A. FIG. 14D illustrates a connectionportion 130 at which the connection electrode 101C is electricallyconnected to the second electrode 102. In the connection portion 130,the second electrode 102 is provided on and in contact with theconnection electrode 101C and the protective layer 131 is provided tocover the second electrode 102. In addition, the insulating layer 124 isprovided to cover end portions of the connection electrode 101C.

Manufacturing Method Example

An example of a method for manufacturing the display device of oneembodiment of the present invention is described below with reference tothe drawings. Here, description is made with use of the light-emittingapparatus 500 shown in the above structure example. FIGS. 15A to 15F arecross-sectional schematic views of steps in a manufacturing method of adisplay device described below. In FIG. 15A and the like, thecross-sectional schematic views of the connection portion 130 and theperiphery thereof are also illustrated on the right side.

Note that thin films included in the display device (e.g., insulatingfilms, semiconductor films, or conductive films) can be formed by any ofa sputtering method, a chemical vapor deposition (CVD) method, a vacuumevaporation method, a pulsed laser deposition (PLD) method, an atomiclayer deposition (ALD) method, and the like. Examples of the CVD methodinclude a plasma-enhanced chemical vapor deposition (PECVD) method and athermal CVD method. An example of a thermal CVD method is a metalorganic CVD (MOCVD) method.

Alternatively, thin films included in the display device (e.g.,insulating films, semiconductor films, and conductive films) can beformed by a method such as spin coating, dipping, spray coating,ink-jetting, dispensing, screen printing, or offset printing or with adoctor knife, a slit coater, a roll coater, a curtain coater, or a knifecoater.

Thin films included in the display device can be processed by aphotolithography method or the like. Besides, a nanoimprinting method, asandblasting method, a lift-off method, or the like may be used toprocess thin films. Alternatively, island-shaped thin films may bedirectly formed by a film formation method using a shielding mask suchas a metal mask.

There are two typical examples of photolithography methods. In one ofthe methods, a resist mask is formed over a thin film that is to beprocessed, the thin film is processed by etching or the like, and thenthe resist mask is removed. In the other method, a photosensitive thinfilm is formed and then processed into a desired shape by light exposureand development.

As light for exposure in a photolithography method, light with an i-line(with a wavelength of 365 nm), light with a g-line (with a wavelength of436 nm), light with an h-line (with a wavelength of 405 nm), or light inwhich the i-line, the g-line, and the h-line are mixed can be used.Alternatively, ultraviolet light, KrF laser light, ArF laser light, orthe like can be used. Exposure may be performed by liquid immersionexposure technique. As the light for exposure, extreme ultraviolet (EUV)light or X-rays may also be used. Furthermore, instead of the light usedfor the exposure, an electron beam can also be used. It is preferable touse EUV, X-rays, or an electron beam because extremely minute processingcan be performed. Note that a photomask is not needed when exposure isperformed by scanning with a beam such as an electron beam.

For etching of thin films, a dry etching method, a wet etching method, asandblast method, or the like can be used.

[Preparation for Substrate 100]

A substrate that has heat resistance high enough to withstand at leastheat treatment performed later can be used as the substrate 100. When aninsulating substrate is used as the substrate 100, a glass substrate, aquartz substrate, a sapphire substrate, a ceramic substrate, an organicresin substrate, or the like can be used. Alternatively, a semiconductorsubstrate can be used. For example, a single crystal semiconductorsubstrate or a polycrystalline semiconductor substrate of silicon,silicon carbide, or the like; a compound semiconductor substrate ofsilicon germanium or the like; an SOI substrate; or the like can beused.

As the substrate 100, it is particularly preferable to use thesemiconductor substrate or the insulating substrate over which asemiconductor circuit including a semiconductor element such as atransistor is formed. The semiconductor circuit preferably forms a pixelcircuit, a gate line driver circuit (a gate driver), a source linedriver circuit (a source driver), or the like. In addition to the above,an arithmetic circuit, a memory circuit, or the like may be formed.

[Formation of First Electrodes 101R, 101G, and 101B, and ConnectionElectrode 101C]

Next, the first electrodes 101R, 101G, and 101B, and the connectionelectrode 101C are formed over the substrate 100. First, a conductivefilm to be an anode (a pixel electrode) is formed, a resist mask isformed by a photolithography method, and an unnecessary portion of theconductive film is removed by etching. After that, the resist mask isremoved to form the first electrodes 101R, 101G, and 101B.

In the case where a conductive film that reflects visible light is usedas each pixel electrode, it is preferable to use a material (e.g.,silver or aluminum) having high reflectance in the whole wavelengthrange of visible light. This can increase both light extractionefficiency of the light-emitting devices and color reproducibility. Inthe case where a conductive film that reflects visible light is used aseach pixel electrode, what is called a top-emission light-emittingapparatus in which light is extracted in the direction opposite to thesubstrate can be obtained. In the case where a conductive film thattransmits light is used as each pixel electrode, what is called abottom-emission light-emitting apparatus in which light is extracted inthe direction of the substrate can be obtained.

[Formation of Insulating Layer 124]

Then, the insulating layer 124 is provided to cover end portions of thefirst electrode 101R, the first electrode 101G, and the first electrode101B (FIG. 15A). An organic insulating film or an inorganic insulatingfilm can be used as the insulating layer 124. The end portions of theinsulating layer 124 are preferably tapered to improve step coveragewith an EL film to be formed later. In particular, when an organicinsulating film is used, a photosensitive material is preferably used sothat the shape of the end portions can be easily controlled by theconditions of light exposure and development. In the case where theinsulating layer 124 is not provided, the distance between thelight-emitting devices can be further reduced to offer a light-emittingapparatus with higher resolution.

[Formation of EL Layer 120Rb]

Subsequently, the EL layer 120Rb, which is to be the EL layer 120R, isformed over the first electrode 101R, the first electrode 101G, thefirst electrode 101B, and the insulating layer 124.

The EL layer 120Rb includes at least a light-emitting layer containing alight-emitting material and a hole-transport layer. The EL layer 120Rbmay have a structure in which one or more films functioning as anelectron-injection layer, an electron-transport layer, acharge-generation layer, and a hole-injection layer are further stacked.The EL layer 120Rb can be formed by, for example, an evaporation method,a sputtering method, an inkjet method, or the like. Without limitationto this, the above-described film formation method can be used asappropriate.

For example, the EL layer 120Rb is preferably a stacked film in which ahole-injection layer, a hole-transport layer, a light-emitting layer,and an electron-transport layer are stacked in this order. In that case,a film including the electron-injection layer 115 can be used as the ELlayer formed later. In the light-emitting apparatus of one embodiment ofthe present invention, the electron-transport layer is provided to coverthe light-emitting layer, which can inhibit the light-emitting layerfrom being damaged by a subsequent photolithography step or the like, sothat a highly reliable light-emitting device can be fabricated.

The EL layer 120Rb is preferably formed so as not to overlap with theconnection electrode 101C. For example, in the case where the EL layer120Rb is formed by an evaporation method (or a sputtering method), it ispreferable that the EL layer 120Rb be formed using a shielding mask soas not to be formed over the connection electrode 101C, or the EL layer120Rb be removed in a later etching step.

[Formation of Sacrificial Film 144 a]

Then, the sacrificial film 144 a is formed to cover the EL layer 120Rb.The sacrificial film 144 a is provided in contact with a top surface ofthe connection electrode 101C.

As the sacrificial film 144 a, it is possible to use a film highlyresistant to etching treatment performed on various EL films such as theEL layer 120Rb, i.e., a film having high etching selectivity withrespect to the EL film. Furthermore, as the sacrificial film 144 a, itis possible to use a film having high etching selectivity with respectto a protective film such as a protective film 146 a described later.Moreover, as the sacrificial film 144 a, it is possible to use a filmthat can be removed by a wet etching method, which causes less damage tothe EL film.

The sacrificial film 144 a can be formed using an inorganic film such asa metal film, an alloy film, a metal oxide film, a semiconductor film,or an inorganic insulating film, for example. The sacrificial film 144 acan be formed by any of a variety of film formation methods such as asputtering method, an evaporation method, a CVD method, and an ALDmethod.

The sacrificial film 144 a can be formed using a metal material such asgold, silver, platinum, magnesium, nickel, tungsten, chromium,molybdenum, iron, cobalt, copper, palladium, titanium, aluminum,yttrium, zirconium, or tantalum or an alloy material containing themetal material. It is particularly preferable to use a low-melting-pointmaterial such as aluminum or silver.

Alternatively, the sacrificial film 144 a can be formed using a metaloxide such as an indium-gallium-zinc oxide (In—Ga—Zn oxide, alsoreferred to as IGZO). It is also possible to use indium oxide, indiumzinc oxide (In—Zn oxide), indium tin oxide (In—Sn oxide), indiumtitanium oxide (In—Ti oxide), indium tin zinc oxide (In—Sn—Zn oxide),indium titanium zinc oxide (In—Ti—Zn oxide), indium gallium tin zincoxide (In—Ga—Sn—Zn oxide), or the like. Indium tin oxide containingsilicon, or the like can also be used.

An element M(M is one or more of aluminum, silicon, boron, yttrium,copper, vanadium, beryllium, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, and magnesium) may be used instead of gallium. In particular,M is preferably one or more of gallium, aluminum, and yttrium.

Alternatively, the sacrificial film 144 a can be formed using aninorganic insulating material such as aluminum oxide, hafnium oxide, orsilicon oxide.

The sacrificial film 144 a is preferably formed using a material thatcan be dissolved in a solvent chemically stable with respect to at leastthe uppermost film of the EL layer 120Rb. Specifically, a material thatwill be dissolved in water or alcohol can be suitably used for thesacrificial film 144 a. In formation of the sacrificial film 144 a, itis preferable that application of such a material dissolved in a solventsuch as water or alcohol be performed by a wet process and followed byheat treatment for evaporating the solvent. At this time, the heattreatment is preferably performed under a reduced-pressure atmosphere,in which case the solvent can be removed at a low temperature in a shorttime and thermal damage to the EL layer 120Rb can be accordinglyminimized.

The sacrificial film 144 a can be formed by spin coating, dipping, spraycoating, ink-jetting, dispensing, screen printing, or offset printing,or with a doctor knife, a slit coater, a roll coater, a curtain coater,or a knife coater, for example.

The sacrificial film 144 a can be formed using an organic material suchas polyvinyl alcohol (PVA), polyvinylbutyral, polyvinylpyrrolidone,polyethylene glycol, polyglycerin, pullulan, water-soluble cellulose, oran alcohol-soluble polyamide resin.

[Formation of Protective Film 146 a]

Next, the protective film 146 a is formed over the sacrificial film 144a (FIG. 15B).

The protective film 146 a is a film used as a hard mask when thesacrificial film 144 a is etched later. In a later step of processingthe protective film 146 a, the sacrificial film 144 a is exposed. Thus,the combination of films having high etching selectivity therebetween isselected for the sacrificial film 144 a and the protective film 146 a.It is thus possible to select a film that can be used for the protectivefilm 146 a depending on an etching condition of the sacrificial film 144a and an etching condition of the protective film 146 a.

For example, in the case where dry etching using a gas containingfluorine (also referred to as a fluorine-based gas) is performed for theetching of the protective film 146 a, the protective film 146 a can beformed using silicon, silicon nitride, silicon oxide, tungsten,titanium, molybdenum, tantalum, tantalum nitride, an alloy containingmolybdenum and niobium, an alloy containing molybdenum and tungsten, orthe like. Here, a metal oxide film using IGZO, ITO, or the like is givenas a film having high etching selectivity (that is, enabling low etchingrate) in dry etching using the fluorine-based gas, and such a film canbe used as the sacrificial film 144 a.

Without being limited to the above, a material of the protective film146 a can be selected from a variety of materials depending on etchingconditions of the sacrificial film 144 a and the protective film 146 a.For example, any of the films that can be used for the sacrificial film144 a can be used.

As the protective film 146 a, a nitride film can be used, for example.Specifically, a nitride such as silicon nitride, aluminum nitride,hafnium nitride, titanium nitride, tantalum nitride, tungsten nitride,gallium nitride, or germanium nitride can be used.

As the protective film 146 a, an oxide film can also be used. Typically,it is possible to use a film of an oxide or an oxynitride such assilicon oxide, silicon oxynitride, aluminum oxide, aluminum oxynitride,hafnium oxide, or hafnium oxynitride.

Alternatively, as the protective film 146 a, an organic film that can beused for the EL layer 120Rb or the like can be used. For example, theprotective film 146 a can be formed using the same film as the organicfilm that is used for the EL layer such as the EL layer 120Rb. Use ofsuch an organic film is preferable because the same film formationapparatus can be used for formation of the EL layer 120Rb or the like.

[Formation of Resist Mask 143 a]

Then, the resist mask 143 a is formed in positions over the protectivefilm 146 a that overlap with the first electrode 101R and the connectionelectrode 101C (FIG. 15C).

For the resist mask 143 a, a resist material containing a photosensitiveresin such as a positive type resist material or a negative type resistmaterial can be used.

On the assumption that the resist mask 143 a is formed over thesacrificial film 144 a without the protective film 146 a therebetween,there is a risk of dissolving the EL layer 120Rb due to a solvent of theresist material if a defect such as a pinhole exists in the sacrificialfilm 144 a. Such a defect can be prevented by using the protective film146 a.

In the case where a film that is unlikely to cause a defect such as apinhole is used as the sacrificial film 144 a, the resist mask 143 a maybe formed directly on the sacrificial film 144 a without the protectivefilm 146 a therebetween.

[Etching of Protective Film 146 a]Next, part of the protective film 146a that is not covered with the resist mask 143 a is removed by etching,so that a band-shaped protective layer 147 a is formed. At that time,the protective layer 147 a is formed also over the connection electrode101C.

In the etching of the protective film 146 a, an etching condition withhigh selectively is preferably employed so that the sacrificial film 144a is not removed by the etching. Either wet etching or dry etching canbe performed for the etching of the protective film 146 a. With use ofdry etching, a reduction in a processing pattern of the protective film146 a can be inhibited.

[Removal of Resist Mask 143 a]

Then, the resist mask 143 a is removed (FIG. 15D).

The removal of the resist mask 143 a can be performed by wet etching ordry etching. It is particularly preferable to perform dry etching (alsoreferred to as plasma ashing) using an oxygen gas as an etching gas toremove the resist mask 143 a.

At this time, the removal of the resist mask 143 a is performed in astate where the EL layer 120Rb is covered with the sacrificial film 144a; thus, the EL layer 120Rb is less likely to be affected by theremoval. In particular, when the EL layer 120Rb is exposed to oxygen,the electrical characteristics of the light-emitting device areadversely affected in some cases. Therefore, it is preferable that theEL layer 120Rb be covered with the sacrificial film 144 a when etchingusing an oxygen gas, such as plasma ashing, is performed.

[Etching of Sacrificial Film 144 a]

Next, part of the sacrificial film 144 a that is not covered with theprotective layer 147 a is removed by etching with use of the protectivelayer 147 a as a mask, so that a band-shaped sacrificial layer 145 a isformed (FIG. 15E). At that time, the sacrificial layer 145 a is formedalso over the connection electrode 101C.

Either wet etching or dry etching can be performed for the etching ofthe sacrificial film 144 a. With use of dry etching, a reduction in aprocessing pattern can be inhibited.

[Etching of EL Layer 120Rb and Protective Layer 147 a]

Next, the protective layer 147 a and part of the EL layer 120Rb that isnot covered with the sacrificial layer 145 a are removed by etching atthe same time, so that the band-shaped EL layer 120R is formed (FIG.15F). At that time, the protective layer 147 a over the connectionelectrode 101C is also removed.

The EL layer 120Rb and the protective layer 147 a are preferably etchedby the same treatment so that the process can be simplified to reducethe manufacturing cost of the display device.

For the etching of the EL layer 120Rb, it is particularly preferable toperform dry etching using an etching gas that does not contain oxygen asits main component. This is because the alteration of the EL layer 120Rbis inhibited, and a highly reliable display device can be achieved.Examples of the etching gas that does not contain oxygen as its maincomponent include CF₄, C₄F₈, SF₆, CHF₃, Cl₂, H₂O, BCl₃, or a rare gassuch as H₂ or He. Alternatively, a mixed gas of the above gas and adilute gas that does not contain oxygen can be used the etching gas.

Note that the etching of the EL layer 120Rb and the etching of theprotective layer 147 a may be performed separately. In that case, eitherthe etching of the EL layer 120Rb or the etching of the protective layer147 a may be performed first.

At this step, the EL layer 120R and the connection electrode 101C arecovered with the sacrificial layer 145 a.

[Formation of EL Layer 120Gb]Subsequently, the EL layer 120Gb, which isto be the EL layer 120G, is formed over the sacrificial layer 145 a, theinsulating layer 124, the first electrode 101G, and the first electrode101B. In that case, similarly to the EL layer 120Rb, the EL layer 120Gbis preferably not provided over the connection electrode 101C.

For the formation method of the EL layer 120Gb, the above description ofthe EL layer 120Rb can be referred to.

[Formation of Sacrificial Film 144 b]

Then, the sacrificial film 144 b is formed over the EL layer 120Gb. Thesacrificial film 144 b can be formed in a manner similar to that for thesacrificial film 144 a. In particular, the sacrificial film 144 b andthe sacrificial film 144 a are preferably formed using the samematerial.

At that time, the sacrificial film 144 a is formed also over theconnection electrode 101C so as to cover the sacrificial layer 145 a.

[Formation of Protective Film 146 b]

Next, the protective film 146 b is formed over the sacrificial film 144b. The protective film 146 b can be formed in a manner similar to thatfor the protective film 146 a. In particular, the protective film 146 band the protective film 146 a are preferably formed using the samematerial.

[Formation of Resist Mask 143 b]

Then, the resist mask 143 b is formed in positions over the protectivefilm 146 b that overlap with the first electrode 101G and the connectionelectrode 101C (FIG. 16A).

The resist mask 143 b can be formed in a manner similar to that for theresist mask 143 a.

[Etching of Protective Film 146 b]

Next, part of the protective film 146 b that is not covered with theresist mask 143 b is removed by etching, so that a band-shapedprotective layer 147 b is formed (FIG. 16B). At that time, theprotective layer 147 b is formed also over the connection electrode101C.

For the etching of the protective film 146 b, the above description ofthe protective film 146 a can be referred to.

[Removal of Resist Mask 143 b]

Then, the resist mask 143 b is removed. For the removal of resist mask143 b, the above description of the resist mask 143 a can be referredto.

[Etching of Sacrificial Film 144 b]

Next, part of the sacrificial film 144 b that is not covered with theprotective layer 147 b is removed by etching with use of the protectivelayer 147 b as a mask, so that a band-shaped sacrificial layer 145 b isformed. At that time, the sacrificial layer 145 b is formed also overthe connection electrode 101C. The sacrificial layer 145 a and thesacrificial layer 145 b are stacked over the connection electrode 101C.

For the etching of the sacrificial film 144 b, the above description ofthe sacrificial film 144 a can be referred to.

[Etching of EL Layer 120Gb and Protective Layer 147 b]

Next, the protective layer 147 b and part of the EL layer 120Gb that isnot covered with the sacrificial layer 145 b are removed by etching atthe same time, so that the band-shaped EL layer 120G is formed (FIG.16C). At that time, the protective layer 147 b over the connectionelectrode 101C is also removed.

For the etching of the EL layer 120Gb and the protective layer 147 b,the above description of the EL layer 120Rb and the protective layer 147a can be referred to.

At this time, the EL layer 120R is protected by the sacrificial layer145 a, and thus can be prevented from being damaged in the etching stepof the EL layer 120Gb.

In the above manner, the band-shaped EL layer 120R and the band-shapedEL layer 120G can be separately formed with high alignment accuracy.

[Formation of EL Layer 120B]

The above steps are performed on an EL layer 120Bb (not illustrated),whereby the island-shaped EL layer 120B and an island-shaped sacrificiallayer 145 c can be formed (FIG. 16D).

That is, after the formation of the EL layer 120G, the EL layer 120Bb, asacrificial film 144 c, a protective film 146 c, and a resist mask 143 c(each of which is not illustrated) are sequentially formed. After that,the protective film 146 c is etched to form a protective layer 147 c(not illustrated); then, the resist mask 143 c is removed. Subsequently,the sacrificial film 144 c is etched to form the sacrificial layer 145c. Then, the protective layer 147 c and the EL layer 120Bb are etched toform the band-shaped EL layer 120B.

After the EL layer 120B is formed, the sacrificial layer 145 c is alsoformed over the connection electrode 101C. The sacrificial layer 145 a,the sacrificial layer 145 b, and the sacrificial layer 145 c are stackedover the connection electrode 101C.

[Removal of Sacrificial Layer]

Next, the sacrificial layer 145 a, the sacrificial layer 145 b, and thesacrificial layer 145 c are removed, whereby top surfaces of the ELlayer 120R, the EL layer 120G, and the EL layer 120B are exposed (FIG.16E). At that time, the top surface of the connection electrode 101C isalso exposed.

The sacrificial layer 145 a, the sacrificial layer 145 b, and thesacrificial layer 145 c can be removed by wet etching or dry etching. Atthis time, a method that causes as little damage as possible to the ELlayer 120R, the EL layer 120G, and the EL layer 120B is preferablyemployed. In particular, a wet etching method is preferably used. Forexample, wet etching using a tetramethyl ammonium hydroxide (TMAH)solution, diluted hydrofluoric acid, oxalic acid, phosphoric acid,acetic acid, nitric acid, or a mixed solution thereof is preferablyperformed.

Alternatively, the sacrificial layer 145 a, the sacrificial layer 145 b,and the sacrificial layer 145 c are preferably removed by beingdissolved in a solvent such as water or alcohol. Examples of the alcoholin which the sacrificial layer 145 a, the sacrificial layer 145 b, andthe sacrificial layer 145 c can be dissolved include ethyl alcohol,methyl alcohol, isopropyl alcohol (IPA), and glycerin.

After the sacrificial layer 145 a, the sacrificial layer 145 b, and thesacrificial layer 145 c are removed, drying treatment is preferablyperformed in order to remove water contained in the EL layer 120R, theEL layer 120G, and the EL layer 120B and water adsorbed on the surfacesof the EL layer 120R, the EL layer 120G, and the EL layer 120B. Forexample, heat treatment is preferably performed in an inert gasatmosphere or a reduced-pressure atmosphere. The heat treatment can beperformed at a substrate temperature higher than or equal to 50° C. andlower than or equal to 200° C., preferably higher than or equal to 60°C. and lower than or equal to 150° C., and further preferably higherthan or equal to 70° C. and lower than or equal to 120° C. The heattreatment is preferably performed in a reduced-pressure atmospherebecause drying at a lower temperature is possible.

In the above manner, the EL layer 120R, the EL layer 120G, and the ELlayer 120B can be separately formed.

[Formation of Electron-Injection Layer 115]

Then, the electron-injection layer 115 is formed to cover the EL layer120R, the EL layer 120G, and the EL layer 120B.

The electron-injection layer 115 can be formed in a manner similar tothat for the EL layer 120Rb or the like. In the case where theelectron-injection layer 115 is formed by an evaporation method, theelectron-injection layer 115 is preferably formed using a shielding maskso as not to be formed over the connection electrode 101C.

[Formation of Second Electrode 102]

Then, the second electrode 102 is formed to cover the electron-injectionlayer 115 and the connection electrode 101C (FIG. 16F).

The second electrode 102 can be formed by a method such as anevaporation method or a sputtering method. Alternatively, a film formedby an evaporation method and a film formed by a sputtering method may bestacked. In that case, the second electrode 102 is preferably formed soas to cover a region where the electron-injection layer 115 is formed.That is, a structure in which end portions of the electron-injectionlayer 115 overlap with the second electrode 102 can be obtained. Thesecond electrode 102 is preferably formed using a shielding mask.

The second electrode 102 is electrically connected to the connectionelectrode 101C outside a display region.

[Formation of Protective Layer]

Then, a protective layer is formed over the second electrode 102. Aninorganic insulating film used for the protective layer is preferablyformed by a sputtering method, a PECVD method, or an ALD method. Inparticular, an ALD method is preferable because a film deposited by ALDhas good step coverage and is less likely to cause a defect such as apinhole. An organic insulating film is preferably formed by an inkjetmethod because a uniform film can be formed in a desired area.

In the above manner, the light-emitting apparatus of one embodiment ofthe present invention can be manufactured.

Although the second electrode 102 and the electron-injection layer 115are formed so as to have different top surface shapes, they may beformed in the same region.

Embodiment 4

In this embodiment, an example in which the light-emitting devicedescribed in Embodiment 1 is used for a lighting device will bedescribed with reference to FIGS. 6A and 6B. FIG. 6B is a top view ofthe lighting device, and FIG. 6A is a cross-sectional view taken alongthe line e-f in FIG. 6B.

In the lighting device in this embodiment, an anode 401 is formed over asubstrate 400 which is a support with a light-transmitting property. Theanode 401 corresponds to the first electrode 101 in Embodiment 1. Whenlight is extracted through the anode 401, the anode 401 is formed usinga material having a light-transmitting property.

A pad 412 for applying voltage to a cathode 404 is provided over thesubstrate 400.

An EL layer 403 is formed over the anode 401. The structure of the ELlayer 403 corresponds to, for example, the structure of the EL layer 103in Embodiment 1, or the structure in which the light-emitting units andthe charge-generation layer are combined. Refer to the descriptions forthe structure.

The cathode 404 is formed to cover the EL layer 403. The cathode 404corresponds to the second electrode 102 in Embodiment 1. The cathode 404is formed using a material having high reflectance when light isextracted through the anode 401. The cathode 404 is connected to the pad412, thereby receiving voltage.

As described above, the lighting device described in this embodimentincludes a light-emitting device including the anode 401, the EL layer403, and the cathode 404. Since the light-emitting device is alight-emitting device with high emission efficiency, the lighting devicein this embodiment can have low power consumption.

The substrate 400 provided with the light-emitting device having theabove structure is fixed to a sealing substrate 407 with sealingmaterials 405 and 406 and sealing is performed, whereby the lightingdevice is completed. It is possible to use only either the sealingmaterial 405 or the sealing material 406. The inner sealing material 406(not illustrated in FIG. 6B) can be mixed with a desiccant which enablesmoisture to be adsorbed, increasing reliability.

When parts of the pad 412 and the anode 401 are extended to the outsideof the sealing materials 405 and 406, the extended parts can serve asexternal input terminals. An IC chip 420 mounted with a converter or thelike may be provided over the external input terminals.

The lighting device described in this embodiment includes as an ELelement the light-emitting device described in Embodiment 1; thus, thelighting device can have low power consumption.

This embodiment can be freely combined with any of the otherembodiments.

Embodiment 5

In this embodiment, examples of electronic devices each including thelight-emitting device described in Embodiment 1 will be described. Thelight-emitting device described in Embodiment 1 has high emissionefficiency and low power consumption. As a result, the electronicdevices described in this embodiment can each include a light-emittingportion with low power consumption.

Examples of the electronic device including the above light-emittingdevice include television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, digital cameras,digital video cameras, digital photo frames, cellular phones (alsoreferred to as mobile phones or mobile phone devices), portable gamemachines, portable information terminals, audio playback devices, andlarge game machines such as pachinko machines. Specific examples ofthese electronic devices are shown below.

FIG. 7A shows an example of a television device. In the televisiondevice, a display portion 7103 is incorporated in a housing 7101. Here,the housing 7101 is supported by a stand 7105. Images can be displayedon the display portion 7103, and in the display portion 7103, thelight-emitting devices described in Embodiment 1 are arranged in amatrix.

The television device can be operated with an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110. The light-emitting devices described in Embodiment 1may also be arranged in a matrix in the display portion 7107.

Note that the television device is provided with a receiver, a modem,and the like. With the use of the receiver, a general televisionbroadcast can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) data communication can beperformed.

FIG. 7B1 illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer is manufactured using the light-emitting devices describedin Embodiment 1 and arranged in a matrix in the display portion 7203.The computer illustrated in FIG. 7B1 may have a structure illustrated inFIG. 7B2. A computer illustrated in FIG. 7B2 is provided with a displayportion 7210 instead of the keyboard 7204 and the pointing device 7206.The display portion 7210 is a touch panel, and input operation can beperformed by touching display for input on the display portion 7210 witha finger or a dedicated pen. The display portion 7210 can also displayimages other than the display for input. The display portion 7203 mayalso be a touch panel. Connecting the two screens with a hinge canprevent troubles; for example, the screens can be prevented from beingcracked or broken while the computer is being stored or carried.

FIG. 7C shows an example of a portable terminal. A cellular phone isprovided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the cellular phone hasthe display portion 7402 in which the light-emitting devices describedin Embodiment 1 are arranged in a matrix.

When the display portion 7402 of the portable terminal illustrated inFIG. 7C is touched with a finger or the like, data can be input to theportable terminal. In this case, operations such as making a call andcreating an e-mail can be performed by touching the display portion 7402with a finger or the like.

The display portion 7402 has mainly three screen modes. The first modeis a display mode mainly for displaying images. The second mode is aninput mode mainly for inputting data such as text. The third mode is adisplay-and-input mode in which the two modes, the display mode and theinput mode, are combined.

For example, in the case of making a call or creating an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on the screen can be input. In this case, itis preferable to display a keyboard or number buttons on almost theentire screen of the display portion 7402.

When a sensing device including a sensor such as a gyroscope sensor oran acceleration sensor for detecting inclination is provided inside theportable terminal, display on the screen of the display portion 7402 canbe automatically changed in direction by determining the orientation ofthe portable terminal (whether the portable terminal is placedhorizontally or vertically).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. Alternatively,the screen modes can be switched depending on the kind of imagesdisplayed on the display portion 7402. For example, when a signal of animage displayed on the display portion is a signal of moving image data,the screen mode is switched to the display mode. When the signal is asignal of text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed for a certain period while a signal sensed by anoptical sensor in the display portion 7402 is sensed, the screen modemay be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may also function as an image sensor. Forexample, an image of a palm print, a fingerprint, or the like is takenwhen the display portion 7402 is touched with the palm or the finger,whereby personal authentication can be performed. Furthermore, byproviding a backlight or a sensing light source which emitsnear-infrared light in the display portion, an image of a finger vein, apalm vein, or the like can be taken.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 4 asappropriate.

As described above, the application range of the light-emittingapparatus including the light-emitting device described in Embodiment 1or 2 is so wide that this light-emitting apparatus can be used inelectronic devices in a variety of fields. By using the light-emittingdevice described in Embodiment 1 or 2, an electronic device with lowpower consumption can be obtained.

FIG. 8A is a schematic view showing an example of a cleaning robot.

A cleaning robot 5100 includes a display 5101 on its top surface, aplurality of cameras 5102 on its side surface, a brush 5103, andoperation buttons 5104. Although not illustrated, the bottom surface ofthe cleaning robot 5100 is provided with a tire, an inlet, and the like.Furthermore, the cleaning robot 5100 includes various sensors such as aninfrared sensor, an ultrasonic sensor, an acceleration sensor, apiezoelectric sensor, an optical sensor, and a gyroscope sensor. Thecleaning robot 5100 has a wireless communication means.

The cleaning robot 5100 is self-propelled, detects dust 5120, andvacuums the dust through the inlet provided on the bottom surface.

The cleaning robot 5100 can determine whether there is an obstacle suchas a wall, furniture, or a step by analyzing images taken by the cameras5102. When the cleaning robot 5100 detects an object that is likely tobe caught in the brush 5103 (e.g., a wire) by image analysis, therotation of the brush 5103 can be stopped.

The display 5101 can display the remaining capacity of a battery, theamount of collected dust, and the like. The display 5101 may display apath on which the cleaning robot 5100 has run. The display 5101 may be atouch panel, and the operation buttons 5104 may be provided on thedisplay 5101.

The cleaning robot 5100 can communicate with a portable electronicdevice 5140 such as a smartphone. Images taken by the cameras 5102 canbe displayed on the portable electronic device 5140. Accordingly, anowner of the cleaning robot 5100 can monitor his/her room even when theowner is not at home. The owner can also check the display on thedisplay 5101 by the portable electronic device 5140 such as asmartphone.

The light-emitting apparatus of one embodiment of the present inventioncan be used for the display 5101.

A robot 2100 illustrated in FIG. 8B includes an arithmetic device 2110,an illuminance sensor 2101, a microphone 2102, an upper camera 2103, aspeaker 2104, a display 2105, a lower camera 2106, an obstacle sensor2107, and a moving mechanism 2108.

The microphone 2102 has a function of detecting a speaking voice of auser, an environmental sound, and the like. The speaker 2104 has afunction of outputting sound. The robot 2100 can communicate with a userusing the microphone 2102 and the speaker 2104.

The display 2105 has a function of displaying various kinds ofinformation. The robot 2100 can display information desired by a user onthe display 2105. The display 2105 may be provided with a touch panel.Moreover, the display 2105 may be a detachable information terminal, inwhich case charging and data communication can be performed when thedisplay 2105 is set at the home position of the robot 2100.

The upper camera 2103 and the lower camera 2106 each have a function oftaking an image of the surroundings of the robot 2100. The obstaclesensor 2107 can detect an obstacle in the direction where the robot 2100advances with the moving mechanism 2108. The robot 2100 can move safelyby recognizing the surroundings with the upper camera 2103, the lowercamera 2106, and the obstacle sensor 2107. The light-emitting apparatusof one embodiment of the present invention can be used for the display2105.

FIG. 8C shows an example of a goggle-type display. The goggle-typedisplay includes, for example, a housing 5000, a display portion 5001, aspeaker 5003, an LED lamp 5004 (including a power switch or an operationswitch), a connection terminal 5006, a sensor 5007 (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared ray), amicrophone 5008, a display portion 5002, a support 5012, and an earphone5013.

The light-emitting apparatus of one embodiment of the present inventioncan be used for the display portion 5001 and the display portion 5002.

FIG. 9 shows an example in which the light-emitting device described inEmbodiment 1 is used for a table lamp which is a lighting device. Thetable lamp illustrated in FIG. 9 includes a housing 2001 and a lightsource 2002, and the lighting device described in Embodiment 4 may beused for the light source 2002.

FIG. 10 shows an example in which the light-emitting device described inEmbodiment 1 is used for an indoor lighting device 3001. Since thelight-emitting device described in Embodiment 1 has high emissionefficiency, the lighting device can have low power consumption.Furthermore, since the light-emitting device described in Embodiment 1can have a large area, the light-emitting device can be used for alarge-area lighting device. Furthermore, since the light-emitting devicedescribed in Embodiment 1 is thin, the light-emitting device can be usedfor a lighting device having a reduced thickness.

The light-emitting device described in Embodiment 1 can also be used foran automobile windshield or an automobile dashboard. FIG. 11 illustratesa mode in which the light-emitting devices described in Embodiment 1 areused for an automobile windshield and an automobile dashboard. Displayregions 5200 to 5203 each include the light-emitting device described inEmbodiment 1.

The display regions 5200 and 5201 are display devices which are providedin the automobile windshield and include the light-emitting devicedescribed in Embodiment 1. The light-emitting device described inEmbodiment 1 can be formed into what is called a see-through displaydevice, through which the opposite side can be seen, by including ananode and a cathode formed of light-transmitting electrodes. Suchsee-through display devices can be provided even in the automobilewindshield without hindering the view. In the case where a drivingtransistor or the like is provided, a transistor having alight-transmitting property, such as an organic transistor including anorganic semiconductor material or a transistor including an oxidesemiconductor, is preferably used.

The display region 5202 is a display device which is provided in apillar portion and includes the light-emitting device described inEmbodiment 1. The display region 5202 can compensate for the viewhindered by the pillar by displaying an image taken by an imaging unitprovided in the car body. Similarly, the display region 5203 provided inthe dashboard portion can compensate for the view hindered by the carbody by displaying an image taken by an imaging unit provided on theoutside of the automobile; thus, blind areas can be eliminated toenhance the safety. Images that compensate for the areas which a drivercannot see enable the driver to ensure safety easily and comfortably.

The display region 5203 can provide a variety of kinds of information bydisplaying navigation data, the speed, the number of rotations,air-condition setting, and the like. The content or layout of thedisplay can be changed as appropriate according to the user'spreference. Note that such information can also be displayed on thedisplay regions 5200 to 5202. The display regions 5200 to 5203 can alsobe used as lighting devices.

FIGS. 12A and 12B illustrate a foldable portable information terminal5150. The foldable portable information terminal 5150 includes a housing5151, a display region 5152, and a bend portion 5153. FIG. 12Aillustrates the portable information terminal 5150 that is opened. FIG.12B illustrates the portable information terminal that is folded.Despite its large display region 5152, the portable information terminal5150 is compact in size and has excellent portability when folded.

The display region 5152 can be folded in half with the bend portion5153. The bend portion 5153 includes a flexible member and a pluralityof supporting members. When the display region is folded, the flexiblemember expands. The bend portion 5153 has a radius of curvature greaterthan or equal to 2 mm, preferably greater than or equal to 3 mm.

Note that the display region 5152 may be a touch panel (an input/outputdevice) including a touch sensor (an input device). The light-emittingapparatus of one embodiment of the present invention can be used for thedisplay region 5152.

FIGS. 13A to 13C illustrate a foldable portable information terminal9310. FIG. 13A illustrates the portable information terminal 9310 thatis opened. FIG. 13B illustrates the portable information terminal 9310that is being opened or being folded. FIG. 13C illustrates the portableinformation terminal 9310 that is folded. The portable informationterminal 9310 is highly portable when folded. The portable informationterminal 9310 is highly browsable when opened because of a seamlesslarge display region.

A display panel 9311 is supported by three housings 9315 joined togetherby hinges 9313. Note that the display panel 9311 may be a touch panel(an input/output device) including a touch sensor (an input device). Byfolding the display panel 9311 at the hinges 9313 between two housings9315, the portable information terminal 9310 can be reversibly changedin shape from the opened state to the folded state. The light-emittingapparatus of one embodiment of the present invention can be used for thedisplay panel 9311.

Example 1

In this example, a light-emitting device 1, which is a light-emittingdevice of one embodiment of the present invention, and a comparativelight-emitting device 1, which is a comparative light-emitting device,are described. Structural formulae of organic compounds used in thisexample are shown below.

(Fabrication Method of Light-Emitting Device 1)

First, as a reflective electrode, silver (Ag) was deposited over a glasssubstrate to a thickness of 100 nm by a sputtering method, and then, asa transparent electrode, indium tin oxide containing silicon oxide(ITSO) was deposited to a thickness of 10 nm by a sputtering method,whereby the first electrode 101 was formed. The electrode area was setto 4 mm² (2 mm×2 mm). Note that the first electrode 101 is a transparentelectrode, and the transparent electrode and the reflective electrodecan be collectively regarded as the first electrode 101.

Next, in pretreatment for forming the light-emitting device over thesubstrate, a surface of the substrate was washed with water and baked at200° C. for 1 hour, and then UV ozone treatment was performed for 370seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure was reduced to approximately 10-4 Pa,vacuum baking was performed at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate wascooled down for approximately 30 minutes.

Next, the substrate provided with the first electrode 101 was fixed to asubstrate holder provided in the vacuum evaporation apparatus such thatthe surface on which the first electrode 101 was formed faced downward.Then,N-3′,5′-ditertiarybutyl-1,1′-biphenyl-4-yl-N-1,1′-biphenyl-2-yl-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: mmtBuBioFBi) represented by Structural Formula (i) and afluorine-containing electron acceptor material with a molecular weightof 672 (OCHD-003) were deposited on the first electrode 101 to athickness of 10 nm by co-evaporation such that the weight ratio ofmmtBuBioFBi to OCHD-003 was 1:0.1, whereby the hole-injection layer 111was formed.

Over the hole-injection layer 111, mmtBuBioFBi was deposited to athickness of 135 nm by evaporation, whereby the hole-transport layer 112was formed.

Subsequently, over the hole-transport layer 112,N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation:DBfBB1TP) represented by Structural Formula (ii) was deposited to athickness of 10 nm by evaporation, whereby an electron-blocking layerwas formed.

Then, 9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviation:αN-βNPAnth) represented by Structural Formula (iii) and3,10-bis[N-(9-phenyl-9H-carbazol-2-yl)-N-phenylamino]naphtho[2,3-b;6,7-b′]bisbenzofuran(abbreviation: 3,10PCA2Nbf(IV)-02) represented by Structural Formula(iv) were deposited to a thickness of 20 nm by co-evaporation such thatthe weight ratio of αN-βNPAnth to 3,10PCA2Nbf(IV)-02 was 1:0.015,whereby the light-emitting layer 113 was formed.

After that,6-(1,1′-biphenyl-3-yl)-4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenylpyrimidine(abbreviation: 6mBP-4Cz2PPm) represented by Structural Formula (v) wasdeposited to a thickness of 10 nm by evaporation, whereby ahole-blocking layer was formed. Then,2-{(3′,5′-di-tert-butyl)-1,1′-biphenyl-3-yl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mmtBumBPTzn) represented by Structural Formula (vi) and6-methyl-8-quinolinolato-lithium (abbreviation: Li-6mq) represented byStructural Formula (vii) were deposited to a thickness of 20 nm byco-evaporation such that the weight ratio of mmtBumBPTzn to Li-6mq was1:1, whereby the electron-transport layer 114 was formed.

After the electron-transport layer 114 was formed, lithium fluoride(LiF) was deposited to a thickness of 1 nm to form theelectron-injection layer 115, and lastly silver (Ag) and magnesium (Mg)were deposited to a thickness of 15 nm by co-evaporation such that thevolume ratio of Ag to Mg was 10:1 to form the second electrode 102,whereby the light-emitting device 1 was fabricated. Note that the secondelectrode 102 is a transfective electrode having a function ofreflecting light and a function of transmitting light; thus, thelight-emitting device of this example is a top-emission device in whichlight is extracted through the second electrode 102. Furthermore, overthe second electrode 102,5,5′-diphenyl-2,2′-di-5H-[1]benzothieno[3,2-c]carbazole (abbreviation:BisBTc) represented by Structural Formula (viii) was deposited to athickness of 60 nm by evaporation to improve outcoupling efficiency.

(Method for Fabricating Comparative Light-Emitting Device 1)

The comparative light-emitting device 1 was fabricated in a mannersimilar to that of the light-emitting device 1 except that the thicknessof the hole-transport layer was set to 130 nm and the material of thecap layer was changed to4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II) represented by Structural Formula (ix).

The structures of the light-emitting device 1 and the comparativelight-emitting device 1 are listed in the following table.

TABLE 2 Light- Comparative emitting light-emitting Light-emitting devicedevice 1 device 1 Cap layer  60 nm BisBTc DBT3P-II Cathode  15 nm Ag:Mg(10:1) Electron-injection  1 nm LiF layer Electron-transport  20 nmmmtBumBPTzn:Li-6mq layer (1:1) Hole-blocking layer  10 nm 6mBP-4CzP2PmLight-emitting layer  20 nm αN-βNPAnth:3,10PCA2Nbf(IV)-02 (1:0.015)Electron-blocking  10 nm DBfBB1TP layer Hole-transport layer *1mmtBuBioFBi Hole-injection layer  10 nm mmtBuBioFBi:OCHD-003 (1:0.1)Anode  10 nm ITSO Reflective electrode 100 nm Ag *1 Light-emittingdevice 1: 135 nm, Comparative light-emitting device 1: 130 nm

The measured ordinary refractive indexes of mmtBuBioFBi, mmtBumBPTzn,Li-6mq, BisBTc, and DBT3P-II and the measured extinction coefficients ofBisBTc and DBT3P-II are shown in FIG. 18 and FIG. 19. The measurementwas performed with an M-2000U spectroscopic ellipsometer manufactured byJ. A. Woollam Japan Corp. To obtain films used as measurement samples,the material for each layer was deposited to a thickness ofapproximately 50 nm over a quartz substrate by a vacuum evaporationmethod.

From the graphs, mmtBuBioFBi, mmtBumBPTzn, and Li-6mq are low refractiveindex materials having an ordinary refractive index of higher than orequal to 1.50 and lower than or equal to 1.75 in the entire wavelengthrange from 455 nm to 465 nm, and BisBTc is a high refractive indexmaterial having an ordinary refractive index of higher than or equal to1.90 and lower than or equal to 2.40 and an ordinary extinctioncoefficient of higher than or equal to 0 and lower than or equal to 0.01in the entire wavelength range from 455 nm to 465 nm. Furthermore, thepeak wavelength on the longest wavelength side of the ordinaryextinction coefficient is 370 nm, and the alignment order parameter atthis wavelength is −0.23, which is less than −0.1. Note that thelight-emitting device 1 and the comparative light-emitting device 1 areblue light-emitting devices.

The light-emitting device and the comparative light-emitting device weresealed using a glass substrate in a glove box containing a nitrogenatmosphere so as not to be exposed to the air. Specifically, a UVcurable sealing material was applied to surround the devices, only theUV curable sealing material was irradiated with UV while thelight-emitting devices were not irradiated with the UV, and heattreatment was performed at 80° C. under an atmospheric pressure for onehour. Then, the initial characteristics of the light-emitting deviceswere measured.

FIG. 20 shows the luminance-current density characteristics of thelight-emitting device 1 and the comparative light-emitting device 1,FIG. 21 shows the luminance-voltage characteristics thereof, FIG. 22shows the current efficiency-luminance characteristics thereof, FIG. 23shows the current density-voltage characteristics thereof, FIG. 24 showsthe blue index-luminance characteristics thereof, and FIG. 25 shows theemission spectra thereof. Table 3 shows the main characteristics of thelight-emitting device 1 and the comparative light-emitting device 1 at aluminance of approximately 1000 cd/m². The luminance, CIE chromaticity,and emission spectra were measured at normal temperature with an SR-UL1Rspectroradiometer manufactured by TOPCON TECHNOHOUSE CORPORATION.

TABLE 3 Current Current Voltage Current density ChromaticityChromaticity efficiency BI (V) (mA) (mA/cm²) x y (cd/A) (cd/A/y)Light-emitting 4.2 0.50 12.4 0.14 0.05 9.0 190 device 1 Comparative 4.20.47 11.7 0.14 0.05 7.9 171 light-emitting device 1

FIGS. 20 to 25 and Table 3 show that the light-emitting device 1 of oneembodiment of the present invention is a light-emitting device that hasfavorable current efficiency and blue index (BI). In particular, with anextremely high BI of 190 (cd/A/y), the light-emitting device 1 can besaid to have favorable BI. Thus, one embodiment of the present inventionis particularly suitable for a light-emitting device used in a display.

FIG. 26 is a graph showing a change in luminance over driving time at acurrent density of 50 mA/cm². The light-emitting device 1 of oneembodiment of the present invention as well as the comparativelight-emitting device 1 was found to have high reliability.

Next, a plurality of light-emitting devices with different cap layerthicknesses (light-emitting devices 1-1 to 1-4 and comparativelight-emitting devices 1-1 to 1-4) were fabricated, and the relationshipbetween the thickness of the cap layer and the maximum BI was examined.Note that the thickness of the hole-transport layer was adjusted so thatthe maximum BI can be obtained at each cap layer thickness.

<Methods for Fabricating Light-Emitting Devices 1-1 to 1-4>

The light-emitting device 1-1 was fabricated in a manner similar to thatof the light-emitting device 1 except that the thickness of the caplayer was set to 50 nm. The light-emitting device 1-2 was fabricated ina manner similar to that of the light-emitting device 1. Thelight-emitting device 1-3 was fabricated in a manner similar to that ofthe light-emitting device 1 except that the thickness of thehole-transport layer was set to 130 nm and the thickness of the caplayer was set to 70 nm. The light-emitting device 1-4 was fabricated ina manner similar to that of the light-emitting device 1-3 except thatthe thickness of the cap layer was set to 80 nm.

<Methods for Fabricating Comparative Light-Emitting Devices 1-1 to 1-4>

The comparative light-emitting device 1-1 was fabricated in a mannersimilar to that of the comparative light-emitting device 1 except thatthe thickness of the hole-transport layer was set to 135 nm and thethickness of the cap layer was set to 50 nm. The comparativelight-emitting device 1-2 was fabricated in a manner similar to that ofthe comparative light-emitting device 1. The comparative light-emittingdevice 1-3 was fabricated in a manner similar to that of the comparativelight-emitting device 1 except that the thickness of the cap layer wasset to 70 nm. The comparative light-emitting device 1-4 was fabricatedin a manner similar to that of the comparative light-emitting device 1except that the thickness of the cap layer was set to 80 nm.

The structures of the light-emitting devices 1-1 to 1-4 and thecomparative light-emitting devices 1-1 to 1-4 are listed in thefollowing tables.

TABLE 4 Light- Comparative emitting light-emitting Light-emitting devicedevice 1-X device 1-Y Cap layer *3 BisBTc DBT3P-II Cathode  15 nm Ag:Mg(10:1) Electron-injection  1 nm LiF layer Electron-transport  20 nmmmtBumBPTzn:Li-6mq layer (1:1) Hole-blocking layer  10 nm 6mBP-4CzP2PmLight-emitting layer  20 nm αN-βNPAnth:3,10PCA2Nbf(IV)-02 (1:0.015)Electron-blocking  10 nm DBfBB1TP layer Hole-transport layer *2mmtBuBioFBi Hole-injection layer  10 nm mmtBuBioFBi:OCHD-003 (1:0.1)Anode  10 nm ITSO Reflective electrode 100 nm Ag

TABLE 5 Light-emitting Comparative light-emitting device 1-X device 1-Y*2 *3 *2 *3 Thickness Thickness Thickness Thickness of hole- of cap ofhole- of cap X transport layer layer Y transport layer layer 1 135 nm 50nm 1 135 nm 50 nm 2 135 nm 60 nm 2 130 nm 60 nm 3 130 nm 70 nm 3 130 nm70 nm 4 130 nm 80 nm 4 130 nm 80 nm

The results are shown in FIG. 27. When a layer having a low ordinaryrefractive index is provided in a light-emitting device and a cap layeris formed therein using an organic compound having a high ordinaryrefractive index and a low ordinary extinction coefficient, thelight-emitting device can have an extremely favorable BI.

Example 2

In this example, a light-emitting device 10, which is a light-emittingdevice of one embodiment of the present invention, is described.Structural formulae of organic compounds used in this example are shownbelow.

(Fabrication Method of Light-Emitting Device 10)

First, as a reflective electrode, silver (Ag) was deposited over a glasssubstrate to a thickness of 100 nm by a sputtering method, and then, asa transparent electrode, indium tin oxide containing silicon oxide(ITSO) was deposited to a thickness of 5 nm by a sputtering method,whereby the first electrode 101 was formed. The electrode area was setto 4 mm² (2 mm×2 mm). Note that the first electrode 101 is a transparentelectrode, and the transparent electrode and the reflective electrodecan be collectively regarded as the first electrode 101.

Next, in pretreatment for forming the light-emitting device over thesubstrate, a surface of the substrate was washed with water and baked at200° C. for 1 hour, and then UV ozone treatment was performed for 370seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure was reduced to approximately 10-4 Pa,vacuum baking was performed at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate wascooled down for approximately 30 minutes.

Next, the substrate provided with the first electrode 101 was fixed to asubstrate holder provided in the vacuum evaporation apparatus such thatthe surface on which the first electrode 101 was formed faced downward.Then,N-(3″,5′,5″-tri-tert-butyl-1,1′:3′,1″-terphenyl-4-yl)-N-(1,1′-biphenyl-2-yl)-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: mmtBumTPoFBi-04) represented by Structural Formula (x)and a fluorine-containing electron acceptor material with a molecularweight of 672 (OCHD-003) were deposited on the first electrode 101 to athickness of 10 nm by co-evaporation such that the weight ratio ofmmtBumTPoFBi-04 to OCHD-003 was 1:0.1, whereby the hole-injection layer111 was formed.

Over the hole-injection layer 111, mmtBumTPoFBi-04,4,4′-diphenyl-4″-(7;2′-binaphthyl-2-yl)triphenylamine (abbreviation:BBA(βN2)B-03) represented by Structural Formula (xi), andN-3′,5′-ditertiarybutyl-1,1′-biphenyl-4-yl-N-1,1′-biphenyl-2-yl-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: mmtBuBioFBi) represented by Structural Formula (i) weredeposited by evaporation to thicknesses of 52.5 nm, 50 nm, and 40 nm asa first layer, a second layer, and a third layer, respectively, wherebythe hole-transport layer 112 was formed.

Subsequently, over the hole-transport layer 112,N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation:DBfBB1TP) represented by Structural Formula (ii) was deposited to athickness of 10 nm by evaporation, whereby an electron-blocking layerwas formed.

Then, 9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviation:αN-βNPAnth) represented by Structural Formula (iii) and2,12-di(tert-butyl)-5,9-di(4-tert-butylphenyl)-N,N-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazaborin-7-amine(abbreviation: DPhA-tBu4DABNA) represented by Structural Formula (xii)were deposited to a thickness of 20 nm by co-evaporation such that theweight ratio of αN-[βNPAnth to DPhA-tBu4DABNA was 1:0.015, whereby thelight-emitting layer 113 was formed.

After that,6-(1,1′-biphenyl-3-yl)-4-[3,5-bis(9H-carbazol-9-yl)phenyl]-2-phenylpyrimidine(abbreviation: 6mBP-4Cz2PPm) represented by Structural Formula (v) wasdeposited to a thickness of 10 nm by evaporation, whereby ahole-blocking layer was formed. Then,2-{(3′,5′-di-tert-butyl)-1,1′-biphenyl-3-yl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mmtBumBPTzn) represented by Structural Formula (vi) and6-methyl-8-quinolinolato-lithium (abbreviation: Li-6mq) represented byStructural Formula (vii) were deposited to a thickness of 20 nm byco-evaporation such that the weight ratio of mmtBumBPTzn to Li-6mq was1:1, whereby the electron-transport layer 114 was formed.

After the electron-transport layer 114 was formed, lithium fluoride(LiF) was deposited to a thickness of 1 nm by evaporation to form theelectron-injection layer 115, and lastly silver (Ag) and magnesium (Mg)were deposited to a thickness of 15 nm by co-evaporation such that thevolume ratio of Ag to Mg was 1:0.1 to form the second electrode 102,whereby the light-emitting device 10 was fabricated. Note that thesecond electrode 102 is a transflective electrode having a function ofreflecting light and a function of transmitting light; thus, thelight-emitting device of this example is a top-emission device in whichlight is extracted through the second electrode 102. Furthermore, overthe second electrode 102,5,5′-diphenyl-2,2′-di-5H-[1]benzothieno[3,2-c]carbazole (abbreviation:BisBTc) represented by Structural Formula (viii) was deposited to athickness of 65 nm by evaporation to improve outcoupling efficiency.

The structure of the light-emitting device 10 is listed in the followingtable.

TABLE 6 Light-emitting device 10 Cap layer   65 nm BisBTc Cathode   15nm Ag:Mg (10:1) Electron-injection   1 nm LiF layer Electron-transport  20 nm mmtBumBPTzn:Li-6mq layer (1:1) Hole-blocking layer   10 nm6mBP-4CzP2Pm Light-emitting layer   20 nm αN-βNPAnth:DPhA-tBu4DABNA(1:0.015) Electron-blocking   10 nm DBfBB1TP layer Hole- 3   40 nmmmtBuBioFBi transport 2   50 nm BBA(βN2)B-03 layer 1 52.5 nmmmtBumTPoFBi-04 Hole-injection layer   10 nm mmtBumTPoFBi04:OCHD-003(1:0.1) Anode   5 nm ITSO Reflective electrode  100 nm Ag

The measured refractive indexes of mmtBumTPoFBi-04 and BBA(βN2)B-03 areshown in FIG. 28. The measurement was performed with an M-2000Uspectroscopic ellipsometer manufactured by J. A. Woollam Japan Corp. Toobtain films used as measurement samples, the material for each layerwas deposited to a thickness of approximately 50 nm over a quartzsubstrate by a vacuum evaporation method. Note that the refractiveindexes of mmtBuBioFBi, mmtBumBPTzn, Li-6mq, and BisBTc and theextinction coefficient of BisBTc are shown in FIG. 18 and FIG. 19.

From FIGS. 18, 19, and 28, mmtBumTPoFBi-04, mmtBuBioFBi, mmtBumBPTzn,and Li-6mq are low refractive index materials having an ordinaryrefractive index of higher than or equal to 1.50 and lower than or equalto 1.75 in the entire wavelength range from 455 nm to 465 nm, and BisBTcis a high refractive index material having an ordinary refractive indexof higher than or equal to 1.90 and lower than or equal to 2.40 and anordinary extinction coefficient of higher than or equal to 0 and lowerthan or equal to 0.01 in the entire wavelength range from 455 nm to 465nm. Furthermore, the peak wavelength on the longest wavelength side ofthe ordinary extinction coefficient is 370 nm, and the alignment orderparameter at this wavelength is −0.23, which is less than −0.1. Notethat the light-emitting device 10 is a blue light-emitting device.

The light-emitting device 10 was sealed using a glass substrate in aglove box containing a nitrogen atmosphere so as not to be exposed tothe air. Specifically, a UV curable sealing material was applied tosurround the device, only the UV curable sealing material was irradiatedwith UV while the light-emitting device was not irradiated with the UV,and heat treatment was performed at 80° C. under an atmospheric pressurefor one hour. Then, the initial characteristics of the light-emittingdevice were measured.

FIG. 29 shows the luminance-current density characteristics of thelight-emitting device 10, FIG. 30 shows the luminance-voltagecharacteristics thereof, FIG. 31 shows the current efficiency-luminancecharacteristics thereof, FIG. 32 shows the current density-voltagecharacteristics thereof, FIG. 33 shows the blue index-luminancecharacteristics thereof, and FIG. 34 shows the emission spectra thereof.Table 7 shows the main characteristics at a luminance of approximately1000 cd/m². The luminance, CIE chromaticity, and emission spectra weremeasured at normal temperature with an SR-UL1R spectroradiometermanufactured by TOPCON TECHNOHOUSE CORPORATION.

TABLE 7 Current Current Voltage Current density ChromaticityChromaticity efficiency BI (V) (mA) (mA/cm²) x y (cd/A) (cd/A/y)Light-emitting 4.2 0.41 10.4 0.15 0.03 8.2 258 device 10

FIGS. 29 to 34 and Table 7 show that the light-emitting device 10 of oneembodiment of the present invention is a light-emitting device that hasextremely favorable current efficiency and blue index (BI). Inparticular, the BI is as extremely high as more than 250 (cd/A/y) andthe maximum BI is 265 (cd/A/y); thus, the light-emitting device 10 canbe said to have favorable BI. Therefore, one embodiment of the presentinvention is particularly suitable for a light-emitting device used in adisplay.

FIG. 35 is a graph showing a change in luminance over driving time at acurrent density of 50 mA/cm². The light-emitting device 10 of oneembodiment of the present invention was found to have high reliability.

Reference Synthesis Example 1

Described in this synthesis example is a method for synthesizing2-{(3′,5′-di-tert-butyl)-1,1′-biphenyl-3-yl}-4,6-diphenyl-1,3,5-triazine(abbreviation: mmtBumBPTzn) used in Example 1. The structure ofmmtBumBPTzn is shown below.

Step 1: Synthesis of 3-bromo-3′,5′-di-tert-butylbiphenyl

First, 1.0 g (4.3 mmol) of 3,5-di-t-butylphenylboronic acid, 1.5 g (5.2mmol) of 1-bromo-3-iodobenzene, 4.5 mL of 2 mol/L aqueous solution ofpotassium carbonate, 20 mL of toluene, and 3 mL of ethanol were put intoa three-neck flask and stirred under reduced pressure to be degassed.Furthermore, 52 mg (0.17 mmol) of tris(2-methylphenyl)phosphine(abbreviation: P(o-tolyl)₃) and 10 mg (0.043 mmol) of palladium(II)acetate were added to this mixture, and reacted under a nitrogenatmosphere at 80° C. for 14 hours. After the reaction, extraction withtoluene was performed and the resulting organic layer was dried withmagnesium sulfate. This mixture was subjected to gravity filtration andthe filtrate was purified by silica gel column chromatography (thedeveloping solvent: hexane) to give 1.0 g of a target white solid(yield: 68%). The synthesis scheme of Step 1 is shown below.

Step 2: Synthesis of2-(3′,5′-di-tert-butylbiphenyl-3-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

First, 1.0 g (2.9 mmol) of 3-bromo-3′,5′-di-tert-butylbiphenyl, 0.96 g(3.8 mmol) of bis(pinacolato)diboron, 0.94 g (9.6 mmol) of potassiumacetate, and 30 mL of 1,4-dioxane were put into a three-neck flask andstirred under reduced pressure to be degassed. Furthermore, 0.12 g (0.30mmol) of 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl and 0.12 g(0.15 mmol) of [1,1′-bis(diphenylphosphino)ferrocene]palladium(II)dichloride dichloromethane adduct (abbreviation: Pd(dppf)₂Cl₂—CH₂Cl₂)were added to this mixture, and reacted under a nitrogen atmosphere at110° C. for 24 hours. After the reaction, extraction with toluene wasperformed and the resulting organic layer was dried with magnesiumsulfate. This mixture was subjected to gravity filtration and thefiltrate was purified by silica gel column chromatography (thedeveloping solvent: toluene) to give 0.89 g of a target yellow oil(yield: 78%). The synthesis scheme of Step 2 is shown below.

Step 3: Synthesis of mmtBumBPTzn

First, 1.5 g (5.6 mmol) of 4,6-diphenyl-2-chloro-1,3,5-triazine, 2.4 g(6.2 mmol) of2-(3′,5′-di-tert-butylphenyl-3-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,2.4 g (11 mmol) of tripotassium phosphate, 10 mL of water, 28 mL oftoluene, and 10 mL of 1,4-dioxane were put into a three-neck flask andstirred under reduced pressure to be degassed. Furthermore, 13 mg (0.056mmol) of palladium(II) acetate and 34 mg (0.11 mmol) oftris(2-methylphenyl)phosphine were added to this mixture, and heated andrefluxed under a nitrogen atmosphere for 14 hours. After the reaction,extraction with ethyl acetate was performed and the resulting organiclayer was removed with magnesium sulfate. This mixture was subjected togravity filtration and the filtrate was purified by silica gel columnchromatography (the developing solvent, chloroform:hexane=1:5 changed to1:3). The obtained solid was recrystallized with hexane to give 2.0 g ofa target white solid (yield: 51%). The synthesis scheme of Step 3 isshown below.

By a train sublimation method, 2.0 g of the obtained white solid waspurified by sublimation under an argon gas stream at a pressure of 3.4Pa and a temperature of 220° C. The solid was heated. After thesublimation purification, 1.8 g of a target white solid was obtained ata collection rate of 80%.

Analysis results by nuclear magnetic resonance spectroscopy (¹H-NMR) ofthe white solid obtained in Step 3 are shown below. The results revealthat mmtBumBPTzn was obtained in this example.

¹H NMR (CDCl3, 300 MHz): δ=1.44 (s, 18H), 7.51-7.68 (m, 10H), 7.83 (d,1H), 8.73-8.81 (m, 5H), 9.01 (s, 1H).

Reference Synthesis Example 2

Described in this example is a method for synthesizing6-methyl-8-quinolinolato-lithium (abbreviation: Li-6mq) used inExample 1. The structural formula of Li-6mq is shown below.

First, 2.0 g (12.6 mmol) of 8-hydroxy-6-methylquinoline and 130 mL ofdehydrated tetrahydrofuran (abbreviation: THF) were put into athree-neck flask and stirred. Then, 10.1 mL (10.1 mmol) of 1M THFsolution of lithium tert-butoxide (abbreviation: tBuOLi) was added tothis solution and stirred at room temperature for 47 hours. The reactedsolution was concentrated to give a yellow solid. Acetonitrile was addedto this solid and subjected to ultrasonic irradiation and filtration, sothat a pale yellow solid was obtained. This washing step was performedtwice. The obtained residue was 1.6 g of pale yellow solid of Li-6mq(yield: 95%). This synthesis scheme is shown below.

Next, the absorption and emission spectra of Li-6mq in a dehydratedacetone solution were measured. The absorption spectrum was measuredwith an ultraviolet-visible light spectrophotometer (V550, manufacturedby JASCO Corporation), and the spectrum of dehydrated acetone alone in aquartz cell was subtracted. The emission spectrum was measured with afluorescence spectrophotometer (FP-8600, produced by JASCO Corporation).

As a result, Li-6mq in the dehydrated acetone solution has an absorptionpeak at 390 nm, and an emission wavelength peak at 540 nm (excitationwavelength: 385 nm).

Reference Synthesis Example 3

Described in this example is a method for synthesizingN-(3″,5′,5″-tri-tert-butyl-1,1′:3′,1″-terphenyl-4-yl)-N-(1,1′-biphenyl-2-yl)-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: mmtBumTPoFBi-04). The structure of mmtBumTPoFBi-04 isshown below.

Step 1: Synthesis of4-bromo-3″,5′,5″-tri-tert-butyl-1,1′:3′,1″-terphenyl

In a three-neck flask were put 9.0 g (20.1 mmol) of2-(3′,5,5′-tri-tert-butyl[1,1′-biphenyl]-3-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,6.8 g (24.1 mmol) of 1-bromo-4-iodobenzene, 8.3 g (60.3 mmol) ofpotassium carbonate, 100 mL of toluene, 40 mL of ethanol, and 30 mL oftap water. The mixture was degassed under reduced pressure, and then theair in the flask was replaced with nitrogen. Then, 91 mg (0.40 mmol) ofpalladium acetate and 211 mg (0.80 mmol) of triphenylphosphine wereadded, and the mixture was heated at 80° C. for approximately 4 hours.After that, the temperature of the flask was lowered to roomtemperature, and the mixture was separated into an organic layer and anaqueous layer. Magnesium sulfate was added to this solution to eliminatemoisture, whereby this solution was concentrated. A hexane solution ofthe obtained solution was purified by silica gel column chromatography,whereby 6.0 g of a target white solid was obtained in a yield of 62.5%.The synthesis scheme of Step 1 is shown below.

Step 2: Synthesis of mmtBumTPoFBi-04

In a three-neck flask were put 3.0 g (6.3 mmol) of4-bromo-3″,5′,5″-tri-tert-butyl-1,1′:3′,1″-terphenyl, 2.3 g (6.3 mmol)of N-(1,1′-biphenyl-4-yl)-N-phenyl-9,9-dimethyl-9H-fluoren-2-amine, 1.8g (18.9 mmol) of sodium-tert-butoxide, and 32 mL of toluene. The mixturewas degassed under reduced pressure, the air in the flask was replacedwith nitrogen, 72 mg (0.13 mmol) ofbis(dibenzylideneacetone)palladium(0) (abbreviation: Pd(dba)₂) and 76 mg(0.38 mmol) of tri-tert-butylphosphine were added thereto, and themixture was heated at 120° C. for approximately 8 hours. After that, thetemperature of the mixture was lowered to approximately 60° C.,approximately 1 mL of water was added, a precipitated solid wasseparated by filtration, and the solid was washed with toluene. Thefiltrate was concentrated, and the obtained toluene solution waspurified by silica gel column chromatography. The obtained solution wasconcentrated to give a condensed toluene solution. Ethanol was added tothis toluene solution and the toluene solution was concentrated underreduced pressure, whereby an ethanol suspension was obtained. Theprecipitate was filtrated at approximately 20° C., and the obtainedsolid was dried at approximately 80° C. under reduced pressure, whereby3.6 g of a target white solid was obtained in a yield of 75%. Thesynthesis scheme of Step 2 is shown below.

Analysis results by nuclear magnetic resonance spectroscopy (¹H-NMR) ofthe white solid obtained in Step 2 are shown below. The results revealthat mmtBumTPoFBi-04 was synthesized in this example.

¹H-NMR. δ (CDCl₃): 7.54-7.56 (m, 1H), 7.53 (dd, 1H, J=1.7 Hz), 7.50 (dd,1H, J=1.7 Hz), 7.27-7.47 (m, 13H), 7.23 (dd, 1H, J=6.3 Hz, 1.2 Hz),7.18-7.19 (m, 2H), 7.08-7.00 (m, 5H), 6.88 (d, 1H, J=1.7 Hz) 6.77 (dd,1H, J=8.0 Hz, 2.3 Hz), 1.42 (s, 9H), 1.39 (s, 18H), 1.29 (s, 6H).

This application is based on Japanese Patent Application Serial No.2021-052207 filed with Japan Patent Office on Mar. 25, 2021, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A material for a cap layer of a light-emittingdevice, the material having an ordinary refractive index of higher thanor equal to 1.90 and lower than or equal to 2.40 and an ordinaryextinction coefficient of higher than or equal to 0 and lower than orequal to 0.01, in an entire wavelength range from 455 nm to 465 nm. 2.The material for a cap layer of a light-emitting device, according toclaim 1, wherein the ordinary refractive index is higher than or equalto 1.95 and lower than or equal to 2.40.
 3. A material for a cap layerof a light-emitting device, the material having an ordinary refractiveindex of higher than or equal to 1.85 and lower than or equal to 2.40and an ordinary extinction coefficient of higher than or equal to 0 andlower than or equal to 0.01, at any wavelength in a range from 500 nm to650 nm.
 4. The material for a cap layer of a light-emitting device,according to claim 3, wherein the ordinary refractive index is higherthan or equal to 1.90 and lower than or equal to 2.40.
 5. The materialfor a cap layer of a light-emitting device, according to claim 1,comprising a condensed ring skeleton having four or more rings or acondensed ring skeleton having five or more rings.
 6. The material for acap layer of a light-emitting device, according to claim 1, comprising asulfur atom.
 7. A cap layer of a light-emitting device, wherein thelight-emitting device comprises an EL layer between a pair of electrodescomprising a light-transmitting electrode, wherein the cap layer is incontact with a surface of the light-transmitting electrode on the sideopposite to the EL layer, and wherein the cap layer comprises a materialhaving an ordinary refractive index of higher than or equal to 1.90 andlower than or equal to 2.40 and an ordinary extinction coefficient ofhigher than or equal to 0 and lower than or equal to 0.01, at anywavelength in a range from 455 nm to 465 nm.
 8. A cap layer of alight-emitting device, wherein the light-emitting device comprises an ELlayer between a pair of electrodes comprising a light-transmittingelectrode, wherein the cap layer is in contact with a surface of thelight-transmitting electrode on the side opposite to the EL layer,wherein light emitted by the light-emitting device has a peak wavelengthof higher than or equal to 455 nm and lower than or equal to 465 nm, andwherein the cap layer comprises a material having an ordinary refractiveindex of higher than or equal to 1.90 and lower than or equal to 2.40and an ordinary extinction coefficient of higher than or equal to 0 andlower than or equal to 0.01, at the peak wavelength.
 9. The cap layeraccording to claim 8, wherein the material has an ordinary extinctioncoefficient of higher than 0.05 at any wavelength in a range from 370 nmto 700 nm.
 10. The cap layer according to claim 8, wherein the ordinaryrefractive index of the material is higher than or equal to 1.95 andlower than or equal to 2.40.
 11. A cap layer of a light-emitting device,wherein the light-emitting device comprises an EL layer between a pairof electrodes comprising a light-transmitting electrode, wherein the caplayer is in contact with a surface of the light-transmitting electrodeon the side opposite to the EL layer, wherein light emitted by thelight-emitting device has a peak wavelength of higher than or equal to500 nm and lower than or equal to 650 nm, and wherein the cap layercomprises a material having an ordinary refractive index of higher thanor equal to 1.85 and lower than or equal to 2.40 and an ordinaryextinction coefficient of higher than or equal to 0 and lower than orequal to 0.01, at the peak wavelength.
 12. The cap layer according toclaim 11, wherein the material has an ordinary extinction coefficient ofhigher than 0.05 at any wavelength in a range from 370 nm to 700 nm. 13.The cap layer according to claim 11, wherein the ordinary refractiveindex of the material is higher than or equal to 1.90 and lower than orequal to 2.40.
 14. The cap layer according to claim 11, wherein thematerial comprises a condensed ring skeleton having four or more ringsor a condensed ring skeleton having five or more rings, and wherein thematerial comprises a sulfur atom.
 15. A light-emitting device comprisingan EL layer between a pair of electrodes, wherein one of the pair ofelectrodes is a light-transmitting electrode, wherein the EL layercomprises at least a light-emitting layer and a low refractive indexlayer, wherein the low refractive index layer is positioned between thelight-emitting layer and the light-transmitting electrode, wherein a caplayer is in contact with a surface of the light-transmitting electrodeon the side opposite to the EL layer, wherein light emitted by thelight-emitting device has a peak wavelength of higher than or equal to455 nm and lower than or equal to 465 nm, wherein the cap layercomprises a high refractive index material having an ordinary refractiveindex of higher than or equal to 1.90 and lower than or equal to 2.40and an ordinary extinction coefficient of higher than or equal to 0 andlower than or equal to 0.01 at the peak wavelength, and wherein the lowrefractive index layer comprises a low refractive index material havingan ordinary refractive index of higher than or equal to 1.50 and lowerthan or equal to 1.75 at the peak wavelength.
 16. The light-emittingdevice according to claim 15, wherein the high refractive index materialhas an ordinary extinction coefficient of higher than 0.01 atwavelengths of lower than or equal to 390 nm.
 17. The light-emittingdevice according to claim 15, wherein the ordinary refractive index ofthe high refractive index material is higher than or equal to 1.95 andlower than or equal to 2.40.
 18. A light-emitting device comprising anEL layer between a pair of electrodes, wherein one of the pair ofelectrodes is a light-transmitting electrode, wherein the EL layercomprises at least a light-emitting layer and a low refractive indexlayer, wherein a cap layer is in contact with a surface of thelight-transmitting electrode on the side opposite to the EL layer,wherein the cap layer comprises a high refractive index material havingan ordinary refractive index of higher than or equal to 1.85 and lowerthan or equal to 2.40 and an ordinary extinction coefficient of higherthan or equal to 0 and lower than or equal to 0.01 at any wavelength ina range from 500 nm to 650 nm, and wherein the low refractive indexlayer comprises a low refractive index material having an ordinaryrefractive index of higher than or equal to 1.45 and lower than or equalto 1.70 in an entire wavelength range from 500 nm to 650 nm.
 19. Alight-emitting device comprising an EL layer between a pair ofelectrodes, wherein one of the pair of electrodes is alight-transmitting electrode, wherein the EL layer comprises at least alight-emitting layer and a low refractive index layer, wherein lightemitted by the light-emitting device has a peak wavelength of higherthan or equal to 500 nm and lower than or equal to 650 nm, wherein a caplayer is in contact with a surface of the light-transmitting electrodeon the side opposite to the EL layer, wherein the cap layer comprises ahigh refractive index material having an ordinary refractive index ofhigher than or equal to 1.85 and lower than or equal to 2.40 and anordinary extinction coefficient of higher than or equal to 0 and lowerthan or equal to 0.01 at the peak wavelength, and wherein the lowrefractive index layer comprises a low refractive index material havingan ordinary refractive index of higher than or equal to 1.45 and lowerthan or equal to 1.70 at the peak wavelength.
 20. The light-emittingdevice according to claim 19, wherein the low refractive index layer ispositioned between the light-emitting layer and the light-transmittingelectrode, wherein the high refractive index material has an ordinaryextinction coefficient of higher than 0.05 at any wavelength in a rangefrom 370 nm to 700 nm, wherein the ordinary refractive index of the highrefractive index material is higher than or equal to 1.90 and lower thanor equal to 2.40, wherein the light-transmitting electrode is a cathode,wherein the low refractive index layer is in an electron-transportregion, wherein the low refractive index layer is an electron-transportlayer, and wherein the low refractive index material is a mixed materialof a material having an electron-transport property and a metal complex.21. The light-emitting device according to claim 19, wherein the otherof the pair of electrodes is a reflective electrode, wherein the ELlayer comprises a second low refractive index layer between thelight-emitting layer and the reflective electrode, and wherein thesecond low refractive index layer comprises a second low refractiveindex material having an ordinary refractive index of higher than orequal to 1.60 and lower than or equal to 1.70 at a peak wavelength oflight emitted by the light-emitting device.
 22. An electronic devicecomprising: the light-emitting device according to claim 19; a sensor;an operation button; and a speaker or a microphone.